Quantitative characterization of igneous rock thermal effect on sandstone reservoir reconstruction based on heat conduction

The X oilfield is the first sandstone reservoir under the influence of igneous rock, which is discovered and put into development in Bohai Sea. Compared with the conventional sandstone reservoir, the oilfield is affected by magmatic activity, the reservoir heterogeneity is serious and the micro pore structure is complex, which results in the poor correlation between mobility calculated by traditional methods and specific oil production index. In order to predict oil well productivity and guide oilfield well location deployment, the quantitative transformation of sandstone reservoir affected by igneous rock is studied in this paper. According to the distribution mode of igneous rock in the reservoir, a permeability model of quantitative characterization for sandstone reservoir permeability is established, in which the influences of heat conduction, reservoir skeleton deformation and stress sensitivity are considered, and then the igneous rock influence on the ground temperature field of surrounding rock is simulated by ANSYS software. According to the relationship between porosity and permeability, the quantitative transformation effect of igneous rock thermal effect on sandstone reservoir is quantitatively characterized. The reservoir temperature field variation law, different baking types and igneous rock thickness influence on the transformation degree of sandstone reservoir are analyzed. Finally, the X oilfield is taken as an example to verify the research method, and the second batch of wells location deployment is successfully guided. The results show that the thermal effect of igneous rock reduces the permeability of reservoir, and the temperature of reservoir increases first and then decreases with time, the rising speed is faster than the falling speed, with the increase in distance from igneous rock, the maximum temperature of reservoir shows a downward trend, in the case of baking on both sides, the heat of igneous rock is greater, which makes the temperature of surrounding reservoir rise more, and the transformation effect on reservoir is more obvious. The influence range of igneous rock thickness on permeability is basically the same, but with the increase in thickness, igneous rock has a greater influence on surrounding rock. The research example of the X oilfield shows that the existence of igneous rock reduces the reservoir physical properties of development wells by 1.2–5.9 times. The correlation between igneous rock physical properties and specific oil production index corrected by this method can reach 0.9478. By avoiding igneous rock, the comparative production of the second batch of development wells is 1.5 times that of the first batch of development wells.

σ 0 Effective stress under initial temperature Φ 0 Porosity under initial temperature

Introduction
Volcanic activity is a geological phenomenon in which magma flows up from the deep part of the earth to the surface. It is also a form of explosive release of heat energy in the earth. Magmatic activity is widely seen in major petroliferous basins all over the world (Einsele et al. 1980;Matos 1992;Othman et al. 2001;Rong et al. 2021;Schofield et al. 2017;Wu et al. 2006). At present, magmatic rocks are encountered in many basins, especially in the area with particularly strong tectonic deformation at the plate edge. After the magma intrudes into the upper layer of the sedimentary basin, the volatile components and liquid solution escapes from the magma enter the surrounding rock under the action of thermal power, which results in water rock reaction and surrounding rock metamorphic. At the same time, high-temperature baking also makes the temperature sensitive surrounding rock metamorphic, in addition, the compression of magma intrusion makes the surrounding rock deform. Therefore, the sedimentary surrounding rock must be affected or transformed by magmatic intrusion. In petroliferous basins, the traditional concept is that magmatic hydrothermal action accelerates the diagenesis process of surrounding rock, worsens the reservoir conditions or destroys the reservoir. Oil and gas exploration should avoid these areas (Gage and Wing 1980;Kingston 1983;Tao 1994). After the Venezuela rapas oil field obtained industrial oil flow in 1953, the oil and gas reservoirs related to magmatic rocks have attracted relevant attention in the industry. Up to now, more than 300 oil and gas reservoirs related to magmatic rocks have been found in the world, most of which belong to early large intrusive oil and gas reservoirs, which are mainly due to the wide distribution range, less eruption periods, large thickness and easy to identify and characterize (Jiang et al. 2011;Kawamoto 2001;Ren et al. 2020). For the oil and gas reservoirs erupted in the late Cenozoic, there are relatively few cases of relevant research and efficient development due to the multiple eruption periods of magmatic rocks, thin reservoir thickness and difficult characterization of clastic rocks. Recent oil and gas exploration shows that magmatic intrusion can form many different types of oil and gas reservoirs. A large number of volcanic rocks or shallow intrusive rocks are developed in petroliferous basins in eastern China. More and more magmatic rocks and metamorphic surrounding rock reservoirs have been found, such as Paleozoic metamorphic rock reservoir and Jurassic volcanic rock reservoir in Xinglongtai buried hill, Songliao Basin (Luo et al. 2005;Rong et al. 2021), intrusive rock reservoir in luo151 well area, Jiyang depression, Bohai Bay Basin (Cao et al. 1999, Liu 2000, Q. and Tang, 1997, Ye et al. 2010, Zhang and Ming 2006, Zhang et al. 2008. With the deepening of oil field exploration and development, the complex types reserves of oil and gas fields are gradually increasing, which plays an increasing role in the oil and gas resources development, especially in the Bohai Bay Basin of China, the clastic rock surrounding rock reservoir affected by magmatic intrusion has become a reserve growth point that cannot be ignored in oil and gas exploration and development (Zhang and Jia-Yu 2003). During the development of sandstone reservoir under the influence of igneous rock, it is difficult to quantitatively characterize the influence of igneous rock on the reservoir, the correlation between mobility and specific production is poor, and the productivity evaluation is difficult. How to realize the efficient development of sandstone reservoir under the igneous rock influence has become a research problem for scholars (Othman et al. 2001). Magma is a kind of high-temperature fluid, and its existence will have a great impact on the geothermal field near the rock mass, which will have a certain impact on the surrounding reservoirs. An in-depth discussion on the thermal effect of magmatic rocks on reservoirs has important guiding significance for the oil and gas reservoirs efficient development in igneous rock development areas.

Influence of magmatic rock on hydrocarbon generation of surrounding rock organic matter
It is generally believed that the role of magmatic rock on surrounding rock includes two aspects. On the one hand, high-temperature magma bakes the organic matter of surrounding rock to carbonize it, on the other hand, magma can improve the terrestrial heat flow value of surrounding rock and accelerate the maturity and evolution of source rock (Duffy et al. 2021;Goodarzi et al. 2019). Specifically, the research on the influence mechanism of magmatic rock on the thermal evolution of organic matter mainly includes the following aspects. First, magmatic heating. Due to the high magmatic temperature, the surrounding rock will produce abnormal high temperature under the action of heat conduction to accelerate the maturity of organic matter. The maximum temperature that can be reached by the surrounding rock is the same as that of magmatic rock, the thickness is related to the thickness of magmatic rock from surrounding rock. The initial temperature of igneous rock is related to factors, such as acidity and alkalinity in the source area and its own lithology. The temperature of basic rock is higher than that of acidic rock, while that of eruptive rock is higher than that of intrusion. Specifically, the initial temperature of basalt is between 1000 and 1255 °C, and that of andesite is between 900 and 1000 °C, the initial temperature of gabbro is between 900 and 1150 °C, that of diorite is between 770 and 850 °C, and that of granite 1 3 is about 700 °C (Cao et al. 2022). Second, the continuous baking time of magma (Q. and Tang, 1997). Duan carried out numerical simulation research and pointed out that the cooling time of columnar magmatic rock with a radius of 500 m can be up to 50,000 years, and the cooling time of columnar magmatic rock with a radius of 1 km can be up to 200,000 years. It has considered that the cooling of magmatic rock is a long-term process, which leads to a long baking time for surrounding rock and further promotes the maturity of organic matter (Duan et al. 2017). Lovering simulated the cooling process of magmatic rocks with different thickness, and considered that it will take 6500 years for the temperature of 200 m thick bedrock to reduce to 10% of the initial temperature. Third, the role of catalyst (Lovering and T., 1935). Some studies have showed that there are a lot of rare gases and metal elements in the magmatic rock, which can be used as a catalyst to promote organic matter hydrocarbon generation during intrusion (Qiang 1998;Shu et al. 2019Shu et al. , 2021. Fourth, Alalade considered the influence of intrusive rock on kerogen and asphalt in organic rich surrounding rock, and pointed out that the rock pyrolysis Tmax value of dark shale near intrusive rock and the percentage of non-fluorescent amorphous organic matter increased significantly (Alalade and Tyson 2013).

Influence range and control factors of magmatic rock on surrounding rock
There is no unified conclusion on the influence range of magmatic rock. It is generally believed that the influence range of magmatic rock is mainly related to the thickness of rock mass and the contact range between magmatic rock and sand body. Carslaw believed that the thermal influence range of magmatic rocks on the upper and lower surrounding rocks is 1.5-3 times the thickness of magmatic rocks (Carslaw and Jaeger 1947). Dow pointed out that the range of magmatic rocks affecting the upper surrounding rocks is weaker than that of the lower surrounding rocks (Dow and Wallace, 1977). Sims studied the magmatic rocks impact on the organic geochemical characteristics of surrounding rock, and pointed out that the upper shale has a narrow impact range but high strength; The upper shale is greatly affected, but the heat impact intensity is weak (Sims and Depaolo 1997). Wang used computer numerical simulation to model the change of surrounding rock geothermal field during magmatic rock cooling, proposed the method of setting the internal heat source boundary of magmatic rock, and sat the influence range of different parameters on surrounding rock (Wang et al. 2007). It is generally perceived that igneous intrusions will locally (100-200% intrusion thickness) reduce sandstone porosity and permeability as heating and movement of pore fluids alters and dissolves framework minerals and cements are precipitated from solution (Duffy et al. 2021).

Study on the influence of magmatic rock on surrounding rock reservoir
The magmatic rock effect on surrounding rock reservoir research is mainly from two perspectives: first, compression deformation. Li believed that magmatic rock can change the physical form of surrounding rock and have compression effect on surrounding rock, which can show compression deformation or brittle fracture in macro view, or a combination of the two, under the action of magmatic rocks, the overlying surrounding rock will produce compressive deformation, and the formed anticline structure is conducive to reservoir formation (Li 2000). Luan believed that magmatic rocks can not only cause secondary fractures and improve reservoir performance, but also dislocation of fracture particles near the reservoir, resulting in fracture healing and rapid reduction of porosity under pressure melting ( Luan and Paterson 1992). Second, heat transfer and hydrothermal metamorphism. It has been believed that the temperature difference between the early magmatic activity and the authigenic sandstone can make the surrounding rock contact with the convective water, and the solution rock can be re produced (Ros 1998). Wu believed that sandstone has poor porosity and it is difficult for thermal convection to occur, however, due to the relative sensitivity of mudstone to temperature, it is prone to recrystallization and various metamorphism under the action of high temperature, which makes the pore structure of the reservoir worse (Wu 1989).
Research shows that in petroliferous basins, magmatism can not only cause relatively strong metamorphism and deformation of surrounding rocks, but also bring a large number of high-temperature hydrothermal fluids, accompanied by abnormally high geothermal gradients, which have a significant impact on the generation, migration and accumulation of oil and gas, as well as the formation and preservation of oil and gas reservoirs (Jiangsu 2000;Li 2000). Previous studied mainly focused on the influence mechanism of magmatism on source rocks, and generally believed that magmatic intrusion accelerates the transformation of organic matter to oil and gas and has a positive impact on oil generation (Dow andWallace, 1977, Simoneit et al. 1978). But there are relatively few studies on the mechanism of intrusion affecting surrounding rock oil and gas reservoirs (Mckinley et al. 2001;Ros 1998). The reason is that (1) there are relatively few clastic rock surrounding rock reservoirs affected by magmatic intrusion in each sedimentary basin, and the distribution range is relatively limited. In addition, the surrounding rock is strongly deformed and metamorphosed under the influence of high-temperature and highpressure hydrothermal fluid brought by magmatic activity.

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The research methods are very different from sedimentary rocks, and there are few studies as a whole; (2)The development characteristics of surrounding rock reservoir are comprehensively controlled by many factors, such as the characteristics of magmatic intrusion (occurrence, nature and scale), the diagenetic stage of surrounding rock during intrusion, the characteristics of surrounding rock before intrusion, and the distance from the intrusion (Girard et al. 1989;Summer and Ayalon 1995), which makes the study of reservoir characteristics more complex. Therefore, the influence mechanism of magma intrusion on surrounding rock has not formed a more systematic research theory and method.
Summarize the above research, the current results have extensive research on igneous rock on surrounding rock, which provides a basis for quantitative research on the impact of magmatic rock on surrounding rock physical properties, but there are still the following problems: (1) The influence mechanism of magmatic rocks on reservoir physical properties is not clear, and the research results of different scholars are quite different.
(2) There are few quantitative studies on the influence of surrounding permeability and igneous field temperature.
(3) Relevant physical property research is mostly used to guide exploration or indoor research, and the research results are lack of verification of development examples.
The innovations of this paper are as follows: first, the influence mechanism of igneous rock on reservoir physical properties is put forward, and the change mechanism of reservoir physical properties after igneous rock intrusion is established under the condition of constant overlying rock pressure; second, the influence of igneous rock on reservoir geothermal field and physical properties is analyzed, including the influence range and degree of igneous rock intrusion on reservoir geothermal field and reservoir physical properties; third, the research results are applied to the X oilfield to guide the well location deployment of the oilfield.

Physical model
The volcano is generally characterized by multi-stage eruption and regional eruption, forming a volcanic rock development area with the same volcanic channel phase, intrusive phase and explosive, as shown in Fig. 1. (1) Volcanic channel phase. Volcanic channel is the main channel for deep magma to rise to the surface. The lithology is mainly basalt, and the top is pyroclastic rock, which is common in the lower part of crater and volcanic mechanism. (2) Intrusive phase. The lithology is mainly basalt, covering a large area in layers or sheets, which is common in the lower part of volcanic institutions. (3) Explosive phase. The lithology is mainly pyroclastic rock with coarse grain size. There are two sources of pyroclastic rocks. One is that the magma is under high pressure under the surface, gushes up to the surface, the pressure is released, the gas overflows, and the explosion leads to the fragmentation of early magmatic rocks to form pyroclastic rocks; The other is that the magma erupts into the air and condenses and falls back to the surface to form volcaniclastic rocks such as volcanic bombs.
According to the distribution mode of igneous rocks and the mutual position relationship between reservoirs, the physical model is simplified and divided into three types: bottom baking, edge baking and edge + bottom baking, as shown in Fig. 2.
According to the physical model established above, take model 1 as an example to mesh the two-dimensional physical model. The mesh is free triangle mesh with a size range of 5-6 m. The model is divided into 2538 meshes. The blue part represents the intrusive magma with a temperature of 1583.15 K (Fig. 3).

Basic assumptions of the model
Based on the elastic theory of porous media and the mechanism of thermal solid coupling, this paper describes the coupling among igneous rocks, heat conduction, reservoir framework and pores. The basic assumptions of the model are as follows: (1) the intrusion of magma is instantaneous, the thermodynamic parameters of magma and surrounding rock are isotropic, the model has no heat exchange with the outside world at the boundary, and the heat absorbed (2) The pressure of overlying rock remains unchanged, and the reservoir transformation of igneous rock to surrounding rock is an irreversible process.
(3) Porous media is regarded as fully saturated and isotropic linear elastomer. The reservoir is elastically deformed and meets the small deformation hypothesis. After skeleton expansion, the pore volume decreases. (4) There is an exponential relationship between porosity and permeability. Figure 4 shows the research roadmap for the mechanism of igneous rocks on reservoir physical properties.

Heat transfer of rock skeleton
In the process of heat conduction from igneous rock to reservoir, it conforms to the law of heat conservation, and the differential equation of heat conduction can be expressed as: where: T represents the temperature, K; t represents the time, a; Φ represents porosity, %, T∕ t represents the change rate of the temperature of a certain area in the system with time, ∇ is a Laplace operator, represents the derivative of the temperature in the conduction direction, and ∇T represents the difference between the temperature of this area and the temperature of the surrounding area. If the adjacent value is large, it is a positive number, otherwise it is a negative number. K c is the thermal conductivity, w/m•K; ρ s is the rock density, kg/m 3 ; c is the specific heat capacity, J/kg•K. The formula shows that when the temperature of a certain area in the system is higher than that of the adjacent area, there will be a process of heat dissipation to the surrounding  Research roadmap for the mechanism of igneous rocks on reservoir physical properties area at the next moment, while the temperature of its own area decreases. The speed of this process is related to the parameters of the reservoir itself.

Relationship between temperature and stress
Assuming that the rock is isotropic, the strain caused by volume thermal expansion is almost linear with the temperature, and the temperature change in the matrix (Yuan et al. 2019) where T is the rock strain caused by temperature. is the coefficient of thermal expansion, 1/K.
Under the action of thermal expansion, the rock will deform, and the stress caused by temperature is expressed as (Yuan et al.2019): where v represents Poisson's ratio, K b = E/3(1-2v) denotes the bulk modulus, E denotes Young's modulus.

Relationship between stress and porosity
The porosity is defined as the ratio of pore volume to total volume.
where V p represents the pore volume, cm 3 ; and V b represents the total volume, cm 3 .
where K p represents the pore elastic modulus.

Relationship between porosity and permeability
According to formula 5, we can get (Yuan et al. 2019): Figure 5 shows the relationship between porosity and permeability which is obtained by experiment, the equation no. 7 is obtained from the statistical regression analysis, which is suitable for the X oilfield in this paper.
where k represents permeability, mD.

Results and discussion
The heat emitted by igneous rock will have a great impact on the geothermal field of surrounding rock, change the pore structure of rock, and then change the reservoir permeability to varying degrees. The traditional calculation process of geothermal field is complex and costly, and there are many restrictive factors in the process of practical application. With the continuous development of computer technology, finite element numerical simulation technology is widely used, calculation results have been obtained. The heat conduction between igneous rock and surrounding rock is a complex process. The ground temperature field of surrounding rock belongs to transient temperature field. With the continuous change of heat exchange, the simulation area is divided into several continuous small areas by finite element method. The size and shape of the area can be different. By numbering each area unit, the continuous transient temperature field is discretized, and the variation characteristics of the temperature field in the simulation area with time are obtained through the variational calculation and solution of the temperature interpolation function in each element. In this paper, the influence of igneous rock on the surrounding rock geothermal field is simulated by ANSYS software, which has the following advantages: first, while simplifying the process of magma heat dissipation, it can reasonably describe the change of transient ground temperature field of surrounding rock. Second, it can calculate the distribution of temperature field at different times at the beginning. On this basis, combined with the relationship curve between porosity and permeability, it can quantitatively characterize the quantitative characterization of igneous rock's transformation of surrounding rock permeability. In the process of modeling, the boundary conditions are input first, including the thickness of igneous rock, distribution range, thickness of reservoir, initial problems of surrounding rock and Permeability mD Porosity % Fig. 5 The relationship between porosity and permeability magma, then the corresponding heat transfer parameters are input, including thermal conductivity, specific heat capacity and density, and then the region into multiple continuous finite elements are divided (Table 1). The size of grid is related to the calculation accuracy, the smaller the grid, the higher the accuracy, but the work of calculation increases at the same time. Finally, through numerical calculation, the change of each grid node in the space with temperature is simulated, the rock deformation is calculate combining with the rock thermal expansion model, the porosity is calculated according to the rock deformation, and the permeability is calculated by using the permeability calculation formula.

Setting of basic parameters
When simulating the heat conduction of magmatic rock, it is necessary to assign parameters. The main parameters of magmatic rock include bedrock thickness, initial temperature of magma, thermal conductivity, specific heat capacity and density. The main parameters of surrounding rock include the initial temperature, thermal conductivity, specific heat capacity, density and actual permeability of surrounding rock. In order to the rationality of parameter assignment, a large number of test results of previous selected parameters or actual parameters are investigated. Figure 6 shows the temperature change with time at a distance of 20 m from the igneous rock when the thickness of igneous rock under the bottom baking type is 10 m, 20 m, 30 m and 100 m, respectively. It can be seen from the figure that the temperature at the distance of 20 m, the igneous rock under different thickness of igneous rock shows the law of first rising and then falling, and the rising speed is faster than the falling speed; with the increase in igneous rock thickness, the peak value of the maximum temperature increases gradually. In the case of igneous rock with thickness of 10, 20, 30 and 100 m, the maximum temperature of 20 m away from igneous rock is 593.78, 701.01, 770.17 K and 940.61 K, respectively; With the increase in igneous rock thickness, the time required to reach the maximum temperature gradually increases. In the case of igneous rock with thickness of 10, 20 , 30 and 100 m, the time required to reach the maximum temperature at 20 m away from igneous rock is 14 , 22, 32 and 88 years, respectively. The main reason is that the greater the thickness of igneous rock, the greater the heat contained, the higher the maximum temperature that a certain point of formation can be heated, and the longer it takes for the whole formation to achieve heat balance. Figure 7 shows the relationship curve between the maximum temperature of reservoir and the distance between reservoir and igneous rock, the thickness of igneous rock under the bottom baking type is 10, 20, 30 and 100 m, respectively. It can be seen from the figure that the maximum temperature of reservoir shows a downward trend with the increase in the distance from igneous rock. Under the condition of different thickness of igneous rock, with the increase in the thickness of igneous rock, the maximum temperature of the surrounding reservoir shows an increasing trend. The maximum temperature of the reservoir corresponding to 10 , 20 , 30 and 100 m are 1024.86 , 1073.33 , 1093.66 and 1122.50 K, respectively. At the same time, the maximum temperature of the reservoir decreases with the increase in distance. When  the thickness of igneous rock is large, the decreasing trend is slow with the increase in distance. The main reason is that the thicker the igneous rock is, the more heat it contains, the more sufficient heat it can provide to the surrounding reservoir, and the higher the maximum temperature of the surrounding reservoir. With the increase in the distance from the igneous rock, the less heat supply is, especially when the thickness of the igneous rock is small. Figure 8 shows the effects of different baking types of bottom + edge baking, edge baking and bottom baking on permeability. It can be seen from the figure that the permeability increases with the increase in the distance from igneous rock. In terms of the impact on surrounding rock, the impact of bottom + edge type igneous rock is greater than that of bottom type igneous rock and edge type igneous rock, and the impact of bottom type igneous rock is equivalent to that of edge type igneous rock. From the physical properties of surrounding rock 20 m away from igneous rock, the permeability of edge type igneous rock and bottom type igneous rock is 89.2 mD, and the permeability of bottom + edge type igneous rock is 79.1 mD. The main reason is that under the condition of baking on both sides, the heat of igneous rock is greater, which makes the temperature of surrounding reservoir rise more, and the transformation effect on reservoir is more obvious. Figure 9 shows the influence of different igneous rock thickness on permeability under the condition of edge baking. It can be seen from the figure that with the increase in igneous rock thickness, the influence of igneous rock on surrounding rock gradually increases. The transformation difference of permeability between different thicknesses first increases and then decreases with the increase in distance from igneous rock. At the contact with igneous rock, the igneous rocks permeability under the influence of 10 , 20, 30 and 100 m thickness is 68.7, 69.8, 70.9 and 73.1 mD, respectively, and the permeability difference between 10 and 100 m igneous rocks is 4.4 mD. At a distance of 20 m from igneous rocks, the permeability under igneous rock thickness of 10, 20, 30 and 100 m are 95.0, 89.1, 85.5 and 76.8 mD, respectively, and the difference of influence of igneous rock with thickness of 10 and 100 m on permeability is 18.2mD. But 100 m away from the igneous rock, the permeability under igneous rock thickness of 10, 20, 30 and 100 m are 107.2, 107.1, 107.0 and 106.9 mD, respectively, and the maximum difference of permeability is 0.3mD. It shows that the influence range of different igneous rock thickness on permeability is basically the same, but with the increase in thickness, igneous rock has a greater influence on surrounding rock. The main reason is that under the action of heat conduction, the temperature will be rapidly transmitted to the surrounding strata, and the temperature difference shows a state of first increasing and then decreasing. The temperature near the igneous rock is close to the igneous rock temperature. After reaching a certain distance, the temperature is basically Fig. 8 Effect of different baking types on permeability Fig. 9 Effect of different igneous rock thickness on permeability Fig. 7 Relationship curve between maximum reservoir temperature and distance between reservoir and igneous rock equal to the average temperature of the whole stratum, and the difference is small.

Geological reservoir characteristics of oil field
The X oilfield is located in the southern Bohai Sea, belonging to the development system of Kenli oilfield group. Structurally, it is located in the north of Laibei low uplift in Bohai Bay Basin and the southern slope zone of middle depression in Huanghekou depression, close to the middle branch of Bonan section of Tanlu fault. The main structural area is a complex fault block structure controlled by a group of large faults, with the characteristics of multiple fault blocks and multiple highs. The strike is mainly near east-west and northeast, and the dip is mainly northeast, northwest and southwest. Multiple sets of oil, gas and water systems are developed vertically and horizontally in the X oilfield. The strata revealed by drilling are Quaternary plain formation, Neogene Minghuazhen formation, Guantao formation, Paleogene Dongying Formation and Shahejie formation from top to bottom. The main oil-bearing series are developed in the Paleogene Dongying formation and Shahejie formation. Volcanic rocks are developed in the Paleogene of the X oilfield. The rock types mainly include basalt, andesite, basaltic andesite, diabase, tuff, tuffaceous sandstone and tuffaceous mudstone. Volcanic rocks mainly affect the distribution of reservoirs in this area by occupying the effective space of clastic rock reservoirs. The reservoirs of the third member of the East and the first and second members of Shahejie formation are mainly affected by volcanic channel phase, overflow phase and subvolcanic phase. The surface crude oil is medium light crude oil, which has the characteristics of low viscosity, medium gum asphaltene content, high wax content, low sulfur content and high freezing point. Formation crude oil has the characteristics of low crude oil viscosity, large ground saturation pressure difference and high dissolved gas oil ratio.
According to the research results of lithofacies model in this area, on the premise of determining the development location, morphological characteristics and seismic facies characteristics of each lithofacies, the igneous rocks are characterized in combination with seismic data. From the description results of igneous rocks, central and fractured volcanic channels are relatively developed in the south block of the oilfield. Igneous rocks have inherited characteristics in the vertical direction, and the development range gradually increases from bottom to top; On the plane, igneous rocks are mainly developed in well areas A, B and C of the oilfield, and there are relatively few other well areas. Igneous rocks within the oilfield generally show the characteristics of independent ring and continuous distribution (Table 1).

Quantitative characterization of permeability
The relative position between igneous rock and reservoir can be simplified into two modes, as shown in Fig. 10.
It can be seen from Fig. 9 that the mode of igneous rock and reservoir in well block A and B belongs to one-sided baking, while the mode of igneous rock and reservoir in Well Block C belongs to two-sided baking. According to the fine characterization results of igneous rock, the statistics of static information and production information of the first batch of 8 development wells in well block A, B and C are carried out, as shown in Table 2.
According to the information in Table 2, the quantitative characterization of the thermal effect of igneous rock on the transformation of sandstone reservoir is carried out, and the corrected permeability is calculated. The comparison diagram between the corrected permeability and the actual permeability is shown in Fig. 11. It can be seen from Fig. 11 that under the influence of igneous rock, the corrected permeability of development well is lower than the actual permeability to a certain extent, the specific reduction degree is related to the type of igneous rock, the distance from igneous rock and the range of igneous rock. On the basis of corrected permeability, the relationship curve between corrected permeability and specific oil production index is drawn, as shown in Fig. 12. It can be seen from the figure that there is a good linear relationship between corrected permeability and specific oil production index, and the square of correlation coefficient is 0.9478, which fully illustrates the reliability of the method.
The subsequent well location deployment was successfully guided. The subsequent development wells avoided igneous rocks appropriately by optimizing the well location. The comparison of the implementation effects of the first batch of development wells and the second batch of development wells in well blocks A, B and C is shown in Fig. 13. From the figure, it can be seen that the distance between the first batch of development wells to avoid igneous rocks is 112 m, and the average value of specific oil production index is 0.35 m 3 / (d ·MPa · m), The average distance of three development wells in the second batch to avoid igneous rock is 173 m, and the average value of specific oil production index is 0.54 m 3 / (d · MPa · m). The specific production of subsequent development wells is significantly higher than that of the first batch of development wells.

Conclusions
In the world, the development of conventional sandstone oil field in the igneous rock development area is the first time. Through detailed geological research, the contact relationship between igneous rocks and sandstone in X Oilfield is described, and the expression of the influence of temperature on reservoir physical properties is established by innovative use the thermal-solid coupling principle, which quantitatively characterizes the influence of temperature on sandstone reservoir after volcanic eruption. The influence of the thickness of igneous rock, the vertical distance between igneous rock and sandstone, and the contact mode between igneous rock and sandstone on the porosity and permeability of sandstone reservoir is analyzed, which provides  corresponding guidance for the well pattern deployment and productivity prediction of similar oilfields. The main conclusions of this study are as follows.
1. Based on the detailed geological description of X Oilfield, the contact modes of three types of igneous rocks and sandstone reservoirs are summarized, and the change of sandstone reservoir temperature after volcanic eruption is simulated innovatively and quantitatively. The greater the thickness of igneous rock near the sandstone reservoir, the greater the impact on the sandstone reservoir. When the thickness of igneous rock is 100 m, the maximum temperature of sandstone reservoir with a vertical distance of 20 m from igneous rock can reach 940.61 K, 2.45 times of the original temperature, so the influence of temperature on sandstone reservoir cannot be ignored. 2. The research innovatively proposes to quantitatively characterize the influence of igneous rock temperature on the physical properties of sandstone reservoirs using the thermal-solid coupling principle. The contact mode between igneous rock and sandstone reservoir is bottom + edge, and the permeability is 79.1mD at the place 20 m vertically away from the igneous rock, which is 28.2mD lower than the original permeability. This contact mode has more serious influence on permeability than the other two modes. At the same time, the greater the thickness of igneous rock, the greater the influence on sandstone reservoir permeability. Taking edge contact as an example, when the thickness of igneous rock is 100 m and the vertical distance from the igneous rock is 20 m, the reservoir permeability is 76.8mD, which is more serious than the 95mD when the thickness of igneous rock is 10 m. 3. The study has important guiding significance for guiding well pattern deployment and productivity prediction of similar oilfields. The physical properties of sandstone reservoirs within 100 m from igneous rocks become poor, and the productivity of production wells is low. To ensure the productivity of production wells, production wells should be at least 100 m away from igneous rocks. The reliability and accuracy of this study are further verified by using the production well data of X oilfield.
Because the fluid in the reservoir occupies a smaller volume than the rock skeleton, and the thermal conductivity is small, the expansion rate is low. The role of rock fluid is not considered in the research process of this paper. In future, the fluid solid coupling model will be introduced in the paper, and the role of fluid in the reservoir will be fully considered, the role of igneous rock thermal effect on reservoir reconstruction will be further analyzed.  Funding This work was financially supported by National Science and technology major project in the 13th five year plan "Bohai oilfield infill adjustment and enhanced oil recovery reservoir engineering technology demonstration" (2016ZX05058001).

Declarations
Conflict of interest Conflict of interest, on behalf of all authors, the corresponding author states that there is no conflict of interest. To be used for non-life science journals.
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