The Possibility of Replacing OBMs with Emulsified Glycol Mud Systems in Drilling Low-Pressure Zones of Iranian Oilfields

Abstract

With increased concerns over the environmental issues regarding the use of oil-based mud (OBM)s, drilling companies in Iran are moving towards implementing less harmful water-based fluids. Due to low toxicity to the environment, effective shale inhibition and considerable cost savings, water-based glycol muds have the highest prospects as alternatives to OBMs in Iranian oilfields. However, designing water-based muds for drilling low-pressure shales may involve a compromise between mud weight optimization and overall environmental and economic advantages offered by these systems. The present study will focus on optimizing the weight of a glycol mud by emulsifying oil in the system and comparing its performance, environmental compatibility and cost with OBMs used in drilling low-pressure zones in Iranian oilfields. Properties of glycol solutions in the presence of oil were also evaluated. An emulsified glycol mud and an OBM with densities of 60 PCF were prepared and compared for their rheology and shale recovery. The shale recovery tests were conducted using shale samples from Maroon oilfield. Possible effects of contamination on the performance of the system were also studied. The glycol system was then treated to recover its diesel content. Overall, the laboratory data were convincing. With very low filtration rates, the emulsified glycol system is a candidate to replace OBMs in reservoir sections. Shale recoveries were comparable to those of OBMs. Compared with a similar OBM, considerable cost savings can be made and the system is more environmentally friendly. However, rheology was more difficult to control and the system was susceptible to contamination. Introduction Since their introduction in the 1930's, oil-based mud (OBM)s have played a major role in drilling troublesome shales. Their development was a milestone in drilling fluid technology as they help to maintain a smooth trouble-free drilling operation through shales. Practically, it is impossible for any water-based mud (WBM) to match the performance of OBMs. Excellent shale inhibition, wellbore stability, lubricity, anti-accretion properties, contamination resistance and possibility of reuse are the main advantages of OBMs over WBMs. Despite the above-mentioned benefits, their toxicity to the environment has limited their application in favor of environmentally-acceptable inhibitive WBMs. Both OBMs and cuttings contaminated with them are toxic discharge to the environment. Regulations restrict the way cuttings contaminated with OBMs can be discharged which may render their use uneconomic. This has paved the way towards replacing them with WBMs which are much more environmentally friendly. However, to replace OBMs, WBMs should have acceptable inhibition, lubricity, filtration and anti-accretion properties while having low toxicity to the environment. Inhibition is of prime importance for any alternative. Calcium, potassium and sodium salts, PHPA, polyglycols, silicates, amine compounds and formats are examples of chemicals which can be used to boost the inhibition properties of WBMs. Some inhibitive WBMs (e.g. Formate muds, KCl/Glycol and KCl/Silicate muds) have inhibition properties comparable to the OBMs. Beside inhibition, lubricity and anti-accretion are the other important properties of High Performance Water-Based Muds which are expected to perform similar to OBMs.

Experimental evaluation of thiamine as a new clay swelling inhibitor

“…Recording this boundary in terms of a function of time gives the appropriate index of bentonite potential for swelling in the inhibitive environment (Moslemizadeh et al 2015). Sodium bentonite Having positive impact on rheological properties, filtration control of drilling fluids Mechanism: formation of plugging film on shale surface Sugars and sugar additives (van Oort 2003) Mechanism: increasing the viscosity of filtrates Cloudy glycols (Chegny et al 2008) Their cloud point (T c ) depends on salinity and glycol concentration Mechanism: when T mud -bit < T c < T rock , at cloud point, glycol comes out from the solution within the formation and ultimately prevents the pressure-induced shale instability; also, it can prevent cutting disintegration by coating Nanoparticles (Sensoy et al 2009;Sharma et al 2012;Riley et al 2012;Li et al 2012;Ji et al 2012;Akhtarmanesh et al 2013;Moslemizadeh and Shadizadeh 2015) Mechanism: closing the pore spaces To close the pore spaces, a high concentration of these particles is needed, which makes the use of these particles noneconomic Henna extract (Moslemizadeh et al 2015) A plant surfactant Mechanism: changing wettability from water-wet to oil-wet Cetyl trimethylammonium bromide (CTAB) (Moslemizadeh et al 2016) A cationic surfactant Mechanism: cation exchange and changing the wettability from waterwet to oil-wet 1-octyl-3-methylimidazolium tetrafluoroborate (Luo et al 2017) An ionic fluid Mechanism: cation exchange and changing the wettability from waterwet to oil-wet Polyamidoamine dendrime (PAMAM) dendrimers (Zhong et al 2015) Intercalation into clay layers Mechanism: multi-adsorption between terminal amine groups and negative sites of clay which keeps clay layers tightly Chitosan quaternary ammonium salt (An et al 2015) An environmentally friendly shale inhibitor. Water-soluble Mechanism: electrostatic attraction and hydrogen bonding Amine-tartaric salt (Chen et al 2017) Compatible with water-based drilling fluids Mechanism: ion exchange, hydrogen bonding and modification of surface wettability of clay toward water Bis(hexamethylene) triamine (Zhong et al 2013) Compatible with water-based drilling fluids Mechanism: ion exchange, hydrogen bonding with siloxane surface of clays and modification of surface wettability of clay toward water Horsetail extract (Barati et al 2016) An environmentally friendly shale inhibitor Mechanism: formation of hydrogen bounding with surfaces of bentonite particles Triterpenoid saponin (Moslemizadeh et al 2017) An environmentally friendly shale inhibitor Mechanism: coating the clay surface and changing wettab...…”

Carboxylated cellulose nanocrystals as environmental-friendly and multi-functional additives for bentonite water-based drilling fluids under high-temperature conditions

“…In these easy-hydrated areas, oil-based drilling uids (OBDFs) have been often applied due to their excellent technical performance, such as good inhibition, lubricity, ltration, and high-temperature resistant (Patel et al 2007). However, OBDFs are expensive, disadvantageous to well logging, and easy to pollute environment(SJ Chegny 2008). Therefore, high-performance WBDFs with environmental consideration are being emphatically studied to replace the OBDFs(M Attia, W Elsorafy and D'Angelo 2010).…”

A biosurfactant for inhibiting clay hydration in aqueous solutions: Applications to petroleum industry

“…[10] However, the application of these fluids has been strongly restricted because of their environmental hazards and high cost. [18,19] Therefore, the use of high performance WBDFs seems a better option to overcome the problems associated with shale instability. Inhibitive WBDFs are obtained through using clay stabilizers or shale inhibitors.…”

“…The use of oil‐based drilling fluids has always been considered a promising alternative to attain the inhibition feature and consequently to overcome the physico‐chemical aspects of wellbore instabilities . However, the application of these fluids has been strongly restricted because of their environmental hazards and high cost . Therefore, the use of high performance WBDFs seems a better option to overcome the problems associated with shale instability.…”