Introduction

The NPT is defined as the time in which the drilling operation ceases in an unplanned way or when the drilling penetration rate becomes excessively low (Dew and Childers 1989). Given the colossal investments in the drilling ventures of oil and gas, whether land or offshore, the drilling time has become intimately reflective of its operational costs. Therefore, reducing the NPT should improve drilling performance and reduce well cost to save money. The NPT concept started in the 1960s, and since then many studies and approaches emerged in an attempt to control lost time to acceptable values.

In Estes (1971), set standardization of bit selection to decrease the NPT using Pareto analysis technique (80/20 rule) to achieve the study objectives. The Pareto principle states that “for many outcomes roughly 80% of consequences come from 20% of the causes” (Pareto and Page 1971). Earlier, this principle has seen many applications in quality control where it was first created. Estes applied this technique in drilling and found that 80% of the losses in the drilling costs come from 20% of the drilling problems. Such finding allowed him to focus on the most cost-effective drilling problems.

Later, Perez et al. (1990) described a successful application of the total quality management methodology for restructuring and improving the drilling organization, generating solutions to improve drilling efficiency, and to solve operational problems encountered in the initial development efforts of a deep onshore field in Venezuela. Then, Bradley et al. (1991) analyzed the drilling time distribution for Gulf of Mexico area from 1985 to 1990, focusing on the cost and the causes of stuck pipe incidents. However, Kadaster et al. (1992) set a systematic approach (extending over more one drilling subsystem) to analyze, evaluate, improve, and re-apply drilling mud, bits, and hydraulic techniques to reduce cost per foot during the drilling operation.

In 2004, Tibiletti et al. stressed the importance of minimizing the NPT. In this work, actual case study from Rashid Petroleum Company (Mediterranean Sea, Egypt) was presented to reduce the NPT in deep water subsea high cost wells. The study included a comparison between the normal operation time and the NPT to show how the NPT has impact on the project performance.

In addition, Gala et al. (2010) reviewed the relation between the NPT and drilling hazards. They developed engineering evaluation processes that helped use of the best drilling tools and techniques available to them to reduce the NPT from 40 to 10%.

Moreover, Everage et al. (2011) reviewed and analyzed a real case study about one of NPT incident of twist-off drill pipe. In this study, the main parameters of risk (probability and cost as a measure of severity) were considered without naming them. This work included a case study about excessive NPT due to normal weight and heavy weight fatigue failures while drilling horizontal wells compared to the vertical wells. The results of the study showed that the failures of heavy weight drill pipe were reduced by 47%, when the American Petroleum Institute standards were applied.

The key performance indicators (KPI) concept played also a major role in supporting drilling performance and evaluating the NPT (Hernandez and Torres 2011). The performance reviewing steps include an immediate action for decision-making process, a balance scorecard application for the required discussion, a periodical review time allocation, and a performance track record. The KPI reflect the performance of a process in achieving its objectives and standards. The main purpose of using KPI is to reduce the drilling costs, eliminate the drilling risks, and maintain the operational integrity (Hernandez and Torres 2011). However, these approaches dwelled on the time value of the NPT without introducing the influence of frequencies or probabilities of happening on the cost of NPT over a common period of time in order to comparatively rate rig performance as far as NPT in a selected number of major drilling operations. The introduction of the notion of probabilities of happening tends to give weights to the happening of the respective values of losses, and when severities (represented by cost) are added, the risk is introduced in the decision which accounts for the uncertainty of happening.

Hurtado and Redlinger (2016) reviewed several NPT field applications and presented a correlation between the drilling efficiency and the successfully proven HSE techniques. They showed that repurposing proven HSE techniques for use outside safety reduces the NPT and improves the drilling efficiency.

Recently, the RM has become a management style conducive to continuous improvement, total quality, and, more generally, business excellence. The RM is an organized process of identifying, evaluating, and handling all risks in order to bring undesired events, in life or in business, to acceptable or tolerable values. In 2004, Main presented the fundamentals of the risk assessment concepts. Later, Khalaf and Abu El Ela (2008) reviewed the basics of risk management and showed that coupling likelihood of happening of an undesired event and its consequences can serve as measure for optimizing operations and is a way toward arranging, recognizing, assessing, choosing, and executing activities to control losses and wastes. As such RM has applications in drilling-NPT analysis.

The structure of the hazard administration has seven phases: (1) defining the problem and putting it in context, (2) analyzing the risks associated with the problem in context, (3) examining options for addressing the risks, (4) making decisions about which options to implement, (5) taking actions to implement the decisions, (6) conducting an evaluation of the action’s results, and (7) documenting the process (Barakat 2018). It is clear that little research work has been tried to extend the concepts of hazard administration or the total quality (TQ) to the NPT on drilling operation and performance. In addition, little research work has been also tried to use the concepts of the risk management to evaluate rig performance. Therefore, the current work intends to borrow the concepts of risk in order to study and assess the NPT performance in the oil and gas drilling operations to find ways to control and reduce the NPT and to evaluate rigs performance according to the risks level of NPT.

Study objectives and methodology

The objectives of this study include the followings:

  1. 1.

    Develop a risk-based general methodology suitable for evaluating rig performance using NPT.

  2. 2.

    Recognize and classify hazards based on analysis of offset wells.

  3. 3.

    Identify and prioritize the hazardous situations related to NPT branches.

  4. 4.

    Analyze, prioritize, and address the major risk based on the existing NPT.

  5. 5.

    Provide recommendation to improve the rigs performance through controlling NPT values.

To achieve these objectives, the authors developed the following methodology as shown in Fig. 1:

Fig. 1
figure 1

Sequence of steps

Full size image
  1. 1.

    Data Collection Drilling data of 250 wells were collected from the operation of 60 onshore rigs for 1 year.

  2. 2.

    Data Classification The collected data were classified according to either productive time or NPT.

  3. 3.

    Data Analysis The collected data were analyzed to identify the categories and types of the NPT, analysis revealed 19 NPT categories in the collected data—these were considered in this study, but the approach can be extended to cover additional NPT categories, provided that enough statistical date are made available.

  4. 4.

    Development of an Analysis and Reporting Software Model A computer program model was developed using Java programming language to get probability of the particular NPT.

  5. 5.

    Model Verification The model was verified by using random samples and test data.

  6. 6.

    Results of the Field Application The oilfield data were used to estimate the probabilities and risks of each NPT category for each rig under study.

  7. 7.

    Rig-NPT Risk Matrix Risk matrix was established for all categories of the NPT and the 60 rigs to present the distribution of the critical and unacceptable high-risk type.

  8. 8.

    Risk Control (RC) The causes of the NPT were analyzed to reduce the NPT, to decrease the probability of NPT, and to improve rig performance.

Data collection, classification, and analysis

The study was carried using data of 60 onshore rigs (Barakat 2018). The work focused on onshore rigs data; however, the model can easily be applied to workover and offshore rigs. The NPT data were collected during the drilling activities for 1 year, through which 250 wells were drilled. The selected onshore rigs have moderate capacity between 1500 and 3000 horsepower. The average daily rig rate is about U$ 40,000/day.

The data collection and analysis were the main entry point for the model. The data source files can be of any type such as .xls, .csv, .xml, .txt, or flat files. Collected data were grouped into 19 categories of the NPT; Table 1 shows the classification of the NPT categories. All categories of NPT data are present in the 60 rigs.

Table 1 Classification and codes of the NPT categories
Full size table

Model structure

It was not easy to deal with huge data without using applicable software to analyze and process the information. The extracted data in this research exceeded one million records for a whole year of rigs activities. Therefore, Java programmed software was used to handle data processing. This software calculates the risk and probability values for the selected rigs according to predefined criteria. The Java software has structure to process data directly from daily drilling report and produces NPT probabilities as output for each one of the 60 rigs.

The program structure consists of four main sections:

  1. 1.

    Source Quicker Loader (SQL) This section loads the data from the external data source files into tables of an oracle database “Master Database.” It supports multiple types of input data files:txt, xml, and flat files.

  2. 2.

    Oracle SQL Database This part holds all loaded data including the Master Data and the Probability Data tables. The Probability Data tables were generated to estimate probability (P) and risk values (R, being the product of probability times cost of the lost time). For each one of the given 60 rigs, there were 19 records representing the majority of operations on the rig daily or monthly operation. Given the size of data available, the records represent precise calculated probability values for all data.

  3. 3.

    TOAD (a Tool for Oracle Application Developers) The database management system is used to create the Master database and the tables which hold the data. It was used to gain access and to control the created oracle database. This tool displays the tables in a well-organized form for better accessibility.

  4. 4.

    Java NetBeans IDE (Integrated Development Environment) It is used for Java development code writing and user interface creation. The developed user interface has a direct connection to the master database on the probability table to fetch probability values calculated for the 60 rigs with respect to the 19 majority operations. The developed Java code uses the probability table to select and to count the total of NPT hours of each rig for each operation and then divides it on the total number of normal operation time as presented in Eq. 1. These data are the probability of the NPT for the selected operation.

    $$P = \frac{\text{NPT}}{{{\text{Normal}}\;{\text{Operation}}\;{\text{Time }}}}$$
    (1)

    where P: frequency of occurrence (probability) of an NPT per year.

Figure 2 illustrates the user interface developed by Java code to facilitate the user interaction with the data. As shown in Fig. 2, the user is able to select the rig, start, and end date, operation type, and whether NPT or not for the probability calculation. The calculated values (for each rig and NPT category) are the total lost time, the total operation duration time, and the probability value.

Fig. 2
figure 2

User interface of the Java reporting module

Full size image

Model validation

The authors used data from five rigs for different types of operations to validate the model, as shown in Table 2. The selection of the validation data was carried out randomly. Then, the probability of the occurrence of each NPT type for each rig was counted manually according to the concept of Eq. 1, and compared with the results of the Java software analysis. It was found that the manually calculated values are consistent with the results of the model. Accordingly, the model was applied to treat the entire data analysis of the current study.

Table 2 Data used for verifying the Java model
Full size table

Model integration with the risk management approach

RM approach was used to analyze and assess the NPT data. Figure 3 shows the steps of the risk management approach. The risk is two-dimensional occasion. Therefore, each hazard or NPT category is distinguished by two parameters of assessment: likelihood (probability) of event of particular undesired occasion, and seriousness of results of such occasion (represents severity) as presented in Eq. 2.

$$R = P*S$$
(2)

where R: risk value, P: frequency of occurrence (probability) of an NPT per year, S: severity of consequences.

Fig. 3
figure 3

Risk management approach

Full size image

The probability of the occurrence of each NPT type (19 NPT category) in each rig (60 rigs) was obtained from Java software analysis. The un it cost of US$ 1667 per hour was taken constant in all cases. The severity value (hourly rate of the rig) was calculated based on that the daily rig rate (U$40,000/day). After that the risk was estimated for each NPT. The risk was classified into four categories according to the criteria presented in Table 3. The calculated risk included four colored areas to differentiate between risks according to their level. The critical and unacceptable type “red” is extreme the highest risk and should be reduced first. The second type of risk is “orange” which is the risk, and it has the second priority to be decreased. The third one is moderate which is the lowest type of risk “yellow,” and it has the least priority to be eliminated. The fourth one “green” is acceptable. After the risk of each NPT category is identified and classified for each rig, Rig-NPT Risk Matrix was developed for the 19 NPT categories and the 60 wells to present the distribution of the critical and unacceptable high-risk type.

Table 3 Risk matrix categories
Full size table

Results of the field applications

NPT analysis

In order to determine the most effective NPT type on rigs which should be controlled, Table 4 was prepared for all NPT categories. The table shows the distribution of the annual operating and NPT of the 60 rigs in 19 operations. The total annual operating time of the 60 rigs is 327,668.65 h. However, the total NPT is 37,051.85 h. Accordingly, the annual cost of all NPT in the 60 rigs is $61,765,434 considering that the hourly rate of the rigs is US$ 1,667.

Table 4 Probability of the NPT in all operations
Full size table

As shown in Table 4, the probability of the occurrence of the NPT in the 60 rigs at each operation is estimated. Then, the probability is sorted from the highest to the lowest (from 0.959 to 0.007). The probability values are divided into three levels. The probabilities from 0.727 to 0.959 is considered the maximum NPT probability that occurred during the de-completion, suspended, fishing, and killing operations. The moderate level is around the probability of 0.5 (maintenance operation). However, the low level of probability is from 0.313 to 0.007. Table 4 indicates that the highest NPT probability comes from the unplanned operations. The unplanned operations are considered sudden orders or problems that happen during the operation time without any planning ahead for it. Also, the probability of maintenance is considered moderate and needs focus to decrease it.

Rig-NPT Risk Matrix

The performance of the rigs was evaluated on the basis of quantitative risk assessment. The principle of risk assessment is used to present the results of probability, severity, and risk. A comparison among 60 rigs was prepared for each kind of NPT (19 types of NPT). The results of the comparisons between all NPT categories in all rigs are presented in Rig-NPT Risk Matrix to show the critical and unacceptable risks.

Due to space limitation, the details of only one category of the NPT in the 60 rigs are presented and discussed. The selected NPT is that during the drilling operation (DRLG). This type was the most common type between rigs in the collected data. As shown in Table 4, the annual cost of this NPT category in the 60 rigs is $28,670,316 out of the total costs of all NPT categories ($61,765,434).

All NPT of drilling mainly happened during rotating time. Table 5 presents the risk values of the NPT during the drilling operation in the 60 rigs obtained from the Java software analysis. Similar tables were extracted for the other 18 NPT categories. Table 5 shows the distribution of the annual NPT of the 60 rigs in the drilling operation. The total NPT in the drilling operations of the 60 rigs is 17,198.75 h. However, the total annual operating time during the drilling operation of the 60 rigs is 164,644.25 h. Accordingly, the estimated annual cost of the NPT in the 60 rigs during the drilling operation is $28,670,316.

Table 5 Risk of the NPT during the drilling operation (DRLG) for the 60 rigs
Full size table

As shown in Table 5, the lowest and highest probabilities values for the NPT during the drilling operation are zeros and 0.27, respectively. The probability of the occurrence is zero in 16 rigs out of the selected 60 rigs (27% of the rigs). Accordingly, 44 rigs out of the 60 rigs (73% of the selected rigs) reported of NPT-related problems. Figure 4 presents the histogram of the risk values between all rigs. The results of Table 5 and Fig. 4 can guide the selection of the characteristics of the other rigs (the 16 rigs) without NPT problems. Therefore, since the severity expressed by the constant hourly rate, the calculated risk (qualified as the cost of the NPT) is influenced by the probability value.

Fig. 4
figure 4

NPT risk values during drilling operation for the 60 rigs

Full size image

In Fig. 4, four risk levels were considered:

  1. 1.

    The histogram shows the unacceptable area of risk for rigs which have risk values higher than US$ 345/h. These rigs (3 rigs) are considered the worst of the fleet and need improvement in order to decrease the NPT of the drilling. They represent 5% of total number of rigs. They have severity cost ranging between $345 and $460 cost $/h.

  2. 2.

    Those in the orange zone are 7% of the total (4 rigs). The severity cost of the drilling operation using these rigs ranges between 230 and 345 U$/h.

  3. 3.

    The rigs in the yellow zone (19 rigs) represent 32% of the fleet. The severity cost of the drilling operation using these rigs ranges between 115 and 230 U$/h.

  4. 4.

    The percentage of rigs in green zone is 30% of total rigs (18 rigs out of 60). The severity cost of the drilling operation using these rigs ranges between 0 and 115 U$/h.

Similar to the above-mentioned risk analysis which was performed for the NPT of the drilling operation, risk assessment for all other NPT categories in all rigs was carried out to prepare Rig-NPT Risk Matrix as shown in Table 6.

Table 6 Rig-NPT Risk Matrix
Full size table

The risk matrix can be used as a benchmark to select the rigs which will continue or not when the oil is devalued. Any horizontal raw in the Rig-NPT Risk Matrix reflects the quality of the performance for each rig. More red boxes in the horizontal raw reflect bad performance for this rig. However, the vertical column reflects the number of occurrences of the same problem for all rigs. From this table, it can be recognized that fishing and milling operations are the common problems in the rigs under study. Higher NPT in these operations occurs more than in the other operations in all rigs, which is expected as these operations are unplanned. For which, further planning is required in order to reduce fishing and milling NPT.

Recommendations and mitigation actions

Strengths, weaknesses, opportunities, and threats (SWOT) Analysis was performed to specify the SWOT for the NPT through verbal interviews of rig crews and other drilling personnel. Table 7 illustrates the results of this SWOT analysis for all categories of the NPT which contributed to the identifying factors involved in the surveyed categories of NPT, a total of 19. It was found that NPT values increase when the negative impact of the following factors (components of the general risk matrix) is high: equipment, personnel/people, environment, and work processes. These factors affected the final system output and determined the final impact on business.

Table 7 SWOT analysis for NPT
Full size table

A set of risk control recommendation were developed for all critical and unacceptable risks in all NPT categories. However, in this paper, the recommendations for the critical and unacceptable risks are only presented for the drilling operation, shown in Table 8, which gives the main reasons of the NPT and the proposed mitigation action for risk control.

Table 8 Mitigation actions and risk control recommendations for the NPT of the drilling operation
Full size table

The implementation of the risk control measures depends on the cost of mitigation which should be ALARP (as low as reasonably practical): lower than the benefit resulting for the risk reduction.

Conclusions

  1. 1.

    The approach of risk assessment helped evaluates rig performance, a necessary step prior to know what and where to improve.

  2. 2.

    Java software model was developed to estimate the probability of the undesired events for the NPT during 1 year of operation for 60 onshore rigs. The model was used to define the highest and lowest probability of the NPT per each NPT category in the drilling operations of all 60 rigs. Such calculation would have been otherwise tedious.

  3. 3.

    The results after applying the model made possible the integration of risk management concepts into the NPT analysis process; such treatment of data has facilitated the development of Rig-NPT Risk Matrix.

  4. 4.

    The inclusion SOWT analysis was helpful for generating sets of case-by-case recommendations that can be extended to NPT incidents in order to improve the rig performance.

Finally, integrating risk management concepts in the NPT analysis introduces uncertainty, represented by the probability parameter, which defines priorities for NPT control.