Introduction

The term drilling mud applies to fluids used to keep up well control and transport drill cuttings from the boreholes to the surface. Drilling mud forms an essential part of drilling operations and the factors considered in proper fluid selection include drilling performance, anticipated well condition, safety of personnel, cost, and mud cuttings disposal (Okoro et al. 2015). Drilling muds must be formulated to minimize problems associated with formation damage, well chemistry and other well instabilities. A notable task confronting mud engineers is how to control and stabilize mud properties to optimize drilling operation at lowest cost possible. The literature has shown that a cluster of mud additives are available to treat most of these significant instabilities in the wellbore, but the question will be how cost effective these additives are per foot drilled, after formulation of drilling mud system.

Ibrahim et al. (2017) outlined some of the functions of a drilling fluid and they also mentioned that some of its functions can contribute to formation damage or permeability impairment. They noted that the selection of suitable mud for individual reservoir is critical. Mud additives contain synthetic and natural chemical compounds that help improve their functions during drilling operation; thus, the additives used for this specific drilling mud are also critical because they define the properties of drilling mud. Ghasemi et al. (2017) observed from their study that the size of the additives present in a mud system can influence the plastic viscosity and yielding point. Elkatatny (2017) emphasized the importance of drilling mud rheological properties and their direct effect on drilling operations.

Agwu and Akpabio (2018) in their study noted that, an effective, environmental friendly and inexpensive drilling mud additive should be ideal for mud formulation. Wajheeuddin and Hossain (2017) highlighted environmental issues and concerns for some of the chemicals used as additives for conventional drilling fluid system, as reasons why non-governmental and governmental agencies are demanding for environmentally friendly mud system. This increase in environmental awareness has made the drilling mud service companies to re-evaluate some of the chemicals and materials used as additives for mud systems. Wajheeuddin and Hossain (2017) proposed that naturally occurring materials with similar properties as these chemicals should be used. In line with their study and findings, some of the materials used in this present study have these characteristics and are also agro-waste materials.

The viscosity green additives

Guar gum powder

Guar gum is a unique substance derived from the Guar plant, with numerous usages. Primarily, there are two types of Guar gum: food grade Guar gum and Industrial grade Guar gum. For the purpose of this study, the industrial grade Guar gum will be used. During drilling operations, Guar gum functions as an excellent additive for mud systems because of its unique characteristics and properties. These properties include, but are not limited to, loss control agent, viscosifiers and polymer (Chudzikowski 1971; Mudgil et al. 2014).

Xanthan gum

It has also appeared as a highly desirable drilling mud additive that helps in minimizing associated well instabilities. Fundamentally, it is a polysaccharide and a biological polymer product from carbohydrates; and can be produced from xanthomonas campestris in controlled condition (Lopes et al. 2015). Some of the most discrete properties of Xanthan gum, which makes it a drilling mud additive, include its use as a stabilizer, emulsifier (in some cases), suspending agent and a thickener for mud systems (Katzbauer 1998; Luvielmo et al. 2016).

Averrhoa carambola L. (Kian)

Narain et al. (2001) and Thomas et al. (2008) in their study gave a detailed analysis and observations on physical and chemical composition of the material in different maturity stages; and also the fruit physico-chemical analysis. Our interest is on the ripe stage. The seed was dried and grinded to its powder form. The powder form was further sieved with a 212 m size sieve and that was the form used for a QAQC test in the mud laboratory (Fig. 1). The Kian powder acted as a thickener during the test process.

Fig. 1
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Averrhoa carambola L. (Kian) fruit and its powdered form

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Brachystegia nigerica (Achi)

Brachystegia nigerica (Achi) belongs to the family of leguminosae and the sub family caesalpiniaceae flowering plants. It grows mainly along river banks or swampy areas, though it can be found in well drained soils. Uwaezuoke et al. (2017) in their study listed viscosity and density as vital properties of a mud system; they also identified some green materials that can act as thickener in a mud system. Atuanya and Ibhadode (2011), after characterization of Brachystegia in their study, concluded that it can be used as reinforcement in polymer matrix composites; thus, its fibers can be used as reinforcements in thermoplastic composites.

Detarium microcarpum (OFFOR)

Detarium microcarpum is particularly associated with dry savannah. It grows naturally in forests, flowers throughout the wet season and bears fruits between November and January. It is nutritious, wholesome, and stimulates the appetite. Thickening usually improves the taste of soups, but most important is their nutritional value in foods. In fact, the nutritional value of soups is determined by the thickening agent used. Thickening agents, or thickeners, are substances which, when added to an aqueous mixture, increase its viscosity.

Methodology

These green materials were processed to powder form and sieved to their finest particle sizes to reduce the amount of solute that would be present in the water-based drilling fluid formed with the materials. QAQC analyses were conducted on these green materials before applying them as possible substitutes for other available viscosifying agents. Standard viscosifying agent (PAC R) was also used to formulate water-based mud for proper comparison. The properties of the formulated mud systems were analyzed using API standard.

A total of four water-based mud systems were formulated for the QAQC analysis and the rheological properties analysis. Both the green materials and PAC R mud systems contained the same amount of additives and were exposed to the same temperature and pressure conditions (Table 1).

Table 1 The water-based mud systems formulation composition
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Results and discussion

Experimental measurements on suitability and compatibility of these green materials as water-based mud fluid viscosifying agent were conducted with respect to API standard. The QAQC test, which is a bench analysis, showed that these materials acted as thickeners and thus, were further used for formulation and mud properties analysis. Their results are presented in Table 2. During formulation, these viscosifiers were applied at different concentrations ranging from 0.5 to 3 ppb; but 2 ppb showed a positive trend in the mud property.

Table 2 Rheological analysis for the water-based mud using the viscosifiers
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The plastic viscosity (PV) depends mainly on the concentration of solids and the viscosity of the base liquid and the yield point (YP) is a measure of the degree of non-Newtonian shear thinning behavior of the mud system. It can be deduced from Fig. 2 that these green materials behaved optimally as viscosifiers for the formulated water-based mud systems under ambient temperature. In addition, the mud system’s behaviour at 150 °F was considered and a reduction in the flow properties were recorded at this increased temperature (Fig. 3). This observation was also recorded by Zhao et al. 2008, Makinde et al. (2011) and Amani and Al-Jubouri (2012) for different viscosifiers used in their studies. Kian and OFFOR green materials were within the API standard at temperature of 150 °F.

Fig. 2
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Flow properties of the water based mud for each viscosifiers at 80 °F

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Fig. 3
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Flow properties of the water based mud for each viscosifier at 120 °F

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Conclusion

In this study, we looked at the suitability of some selected green materials as viscosifiers and the possible effect of temperature on the rheological properties of water-based mud formulated with them. The mud system properties of these green materials were compared with PAC R which is mostly used in the industry for water-based mud systems. Furthermore, the temperatures at which these green materials can be affected were determined. From the results of the experiment, we can say that Kian (Averrhoa carambola L.) has the characteristic of being a substitute for PAC R when beneficiated for water-based drilling fluids.