Utilization of Biopolymers in Water Based Drilling Muds

Abstract

With the increase in energy demand, deeper wells drilling is one of the solutions to fulfill the energy demand, which demands specialized drilling mud formulation. These muds are composed of thermally stable materials that can sustain in high-temperature conditions. Biopolymers are widely used out of various mud additives for improving the rheology and filtration characteristics of mud. Owing to the high temperature and poor thermal stability of such additives, these additives lose their primary functions, resulting in the nonproductive time and irreversible problems. The book chapter highlights the uses of water-based mud, its limitations, and the degradation of biopolymers. Various additives’ significance and susceptibility in harsh borehole conditions have been discussed. The existing additives used for the rheological and filtration characteristics improvements and their shortcomings are presented. Furthermore, the field applications of native and modified polymeric-based mud formulations have been further examined and presented.

1. Introduction

Oil well drilling operation is a common and important process in the petroleum industry. Drilling fluid is an essential operational fluid that plays an exceptional part in drilling engineering. In a rotary drilling operation, drilling fluids are circulated continuously in the wellbore and drilling string [1]. Drilling mud serves a variety of functions, including cleaning and transporting the borehole, maintaining the borehole integrity, reducing formation damage, and cooling and lubricating the tools. Water-based muds are popular due to their low cost and environmental protection requirements. It generally comprises water, clay, and other chemical additives for different purposes.

Various problems are encountered during drilling a wellbore, including clay swelling, shale instability, bit balling, drill string accretion, high torque and drag, differential sticking, and fluid losses. These issues put a substantial cost on the overall drilling operation. These issues further increase with the increase in the wellbore depth. In addition, the conventional muds containing clay, weighting agents, and pH controllers could not be applied in such conditions. This is due to the interaction of such fluids with the clay minerals resulting in the variation in the mechanical properties by clay swelling. Hence, the design and selection of appropriate mud additives are the most critical factors that need to be considered. Oil-based muds (OBMs) are conventionally preferred due to their better thermal stability and nonreactive nature but due to the environmental concerns and their higher costs make them uneconomical. Thus, high-performance water-based containing eco-friendly additives are preferred. The concept of high-performance water-based drilling mud has been suggested for decades. It is a water-based drilling mud with acceptable rheology, minimal filtrate loss, high shale inhibition, good lubricity, and plugging properties [2].

The high-performance water-based mud (HPWBM) system was developed to enhance WBM performance while also providing an eco-friendly alternative to oil-based muds (OBM) while mimicking OBM drilling features. Various laboratory and field applications confirmed the HPWBM in replacing OBM by efficaciously accomplishing the objectives. HPWBMs have been recently developed as OBM alternatives, although not all kinds of HPWBM have been able to replace OBM on more complex wells. With the ever-increasing push for greater environmental performance and greater restrictions on the disposal of OBM cuttings, the petroleum industry is trying to design a WBM that can replicate OBM’s performance [3].

High-performance muds are particularly advantageous to conventional water-based systems because they provide faster penetration rates, enhanced hole cleaning, greater shale inhibition, and improved wellbore stability. The high-performance muds can deliver appropriate rheology and fluid stability under HTHP conditions, withstand high solids loading and deliver a high tolerance to brine or salt contamination, so the high-performance fluid is recommended for drilling the gypsum-salt formations and the reservoirs with natural fractures and inter-bedded shale. Such muds only tolerate operating temperatures up to 300°F because they depend on biopolymer-based viscosifiers. Deeper exploration in extreme high-temperature reservoirs (>300°F) requires new drilling fluid technologies.

2. Drilling mud properties

The success of any drilling fluid is dependent on the composition of the mud additives, which alters the mud properties. The two most common properties, including rheological and filtration, are primarily controlled while designing a drilling mud. Both properties can be improved with the utilization of mud additives. Various additives are added to the drilling to maintain the mud rheological and filtration characteristics. During drilling of the pay zone section, various polymers are added to replace bentonite to minimize the damage due to solids intrusion into the pay zone section. Such bentonite-free muds can form a thin and removable filter cake on the borehole wall and thus reduces the formation damage. Some of the most commonly used biopolymers are xanthan gum, guar gum, diutan gum, cellulose, lignins, and starches.

Generally, the viscosity is maintained lower for such muds, but more focus is paid to the filtration characteristics. It is worth mentioning that most water-based mud has shown best fitting with power-law and Herschel-Bulkley model. The laboratory experiments and field applications have observed that the flow behavior index (n) and consistency index (k) are the primary parameters controlling the cuttings transportation. The lower the flow behavior index and the higher the consistency index will perform better in cuttings transportation.

3. Mud properties modification

Two key parameters of drilling mud are generally investigated, including rheological and mud filtration. Mud rheological properties include plastic viscosity (PV), apparent viscosity (AV), gel strength (GS), yield point (YP), and yield stress (YS), while filtration properties consist of fluid loss volume, filter cake thickness, porosity, and permeability. Both the properties are dependent on the proper mud composition. The clay and polymeric materials generally enhance mud rheology, while the fluid loss additives such as starch and other nano-based materials reduce the fluid loss and cake thickness. Starch is a commonly used additive for improving both the rheological and filtration characteristics of mud.

Shale inhibition is another primary factor that requires attention during the mud design. Wellbore instability due to shale swelling and fluid loss of drilling mud is the main challenge the oil and gas industry faces. Shale is generally a water-sensitive material and causes swelling resulting in other drilling issues. Different additives, including salts and other amine-based materials, have been tested to improve shale stability. Several studies have been conducted to modify mud properties. For instance, a water-based mud was developed using an appropriate amine derivative, poly-ethoxylated alkyl diamine as a potential shale inhibitor agent instead of other conventional alternatives. The developed mud has optimally improved the performance of previously formulated HPWBMs [4].

Shale inhibition of amine derivative was examined using a new procedure, namely WSP, which showed better performance in bentonite-based mud systems. The system was found appropriate and an excellent alternative to OBM and SBM when tested in the South China Sea deepwater well. The mud displayed better performance by excellent shale stability, clay inhibition, lubricity, and high rate of penetration (ROP). The mud showed lower cost due to no issue caused during the drilling operation [5].

4. Biopolymers application in water-based muds

Water-based drilling fluids are an economical and eco-friendly alternative for successfully drilling a wellbore. Both conventional and high-performance muds generally use biopolymers to enhance rheological characteristics, provide acceptable viscosity, suspend solids, and control filtrate loss in the wellbore. A few examples are natural biomaterials derived from plants or microorganisms such as starch, guar, xanthan, and their chemically modified substitutes.

Biopolymers used for drilling fluids can be classified as plant-based or microbial-based, depending on their source. For instance, guar gum and locust bean gum are the most widely used plant-based materials. Guar gum is a nonionic linear polymer obtained from the seeds of the guar plant composed of the sugars galactose and mannose. On the other hand, locust bean gum is isolated from the fruit of the legume Ceratonia siliqua, and its structure is similar to guar except for the ratio of galactose to mannose, which influences its solubility in water. It has been observed that the galactose content directly relates to the water solubility. Thus the guar shows better solubility than locust bean gum.

Another kind of biopolymer that is mostly employed in water-based systems is bacterially produced polymers. Xanthan gum is a typical and mostly used additive of this type. It has a more branched structure than other gums and is very efficient, offering shear-thinning rheological behavior that is almost optimal for drilling fluid applications. Similarly, welan gum is a negatively charged (anionic) gum formed by bacteria belonging to the Alcaligenes genus fermenting sugar. It is observed that it exhibits better viscosity and salt resistance.

Various studies have highlighted the importance of biopolymers for the improvement of mud properties. For example, nitrocellulose-based muds were developed in a study, which showed enhanced rheological and filtration properties. It was used in high-performance, water-based fluids as a renewable, non-hazardous, and cost-effective alternative to synthetic polymers, with the added feature of maintaining and optimizing fluid characteristics [6]. Likewise, diutan gum was used as a drilling mud viscosifier, resulting in retaining their viscosities up to 232°C, when sodium erythorbate, potassium formate, and polyethylene glycol were added to the formulations [7].

5. Role of biopolymers in HPWBMs

Various additives are used in the mud with different dosages to enhance the viscosity of drilling mud. During drilling the pay zone section, the main concern is to reduce the invasion of filtrate and solids into the exposed formation. This invasion can cause irreversible problems that cause multiple folds decline in production. Thus, nondamaging mud containing biopolymer and other acid-soluble materials are added to the mud for drilling of such zones. Various biopolymers, including gums (xanthan, guar, and diutan), lignins, starches (both native and modified), cellulose, etc., are widely used in oil well drilling. These gums have been further modified to increase their thermal stability and salt resistance functionality. Figure 1 shows xanthan, diutan, and guar gum structure.

Figure 1.

Structure of (a) xanthan gum [8], (b) diutan gum [9], and (c) guar gum [10].

Due to the environmental concerns about the usage of huge quantities of chemicals and their disposal issues, the oil industry is looking for bio-based/biodegradable materials with very little or no impact on the environment. Therefore, various waste products and other biomaterials have been investigated to substitute the hazardous chemicals used in recent years. These materials include but are not limited to agarwood waste, rice husk, psyllium husk, and groundnut husk: dates, grass, wood, pistachio shell, mandarin peels, palm tree leaves, green olive pits, Cupressus cones powder, etc. The mentioned materials showed that the mud containing these agents could significantly improve the mud properties. Moreover, the overdependence on such expensive commercial materials is reduced by utilizing such additives. These materials are easily available everywhere, and their proper utilization can reduce the extra cost and ensure environmental cleanliness.

6. Role of nanomaterials in HPWBMs

Nanomaterials are synthesized substances with a size ranging from 1 to 100 nanometers (nm) and are therefore used in very small dimensions. These materials have numerous applications in various fields, including automotive, electronics, pharmaceuticals, etc. In recent years their applications were also observed in the petroleum industry in different areas. In drilling fluids, nanomaterials have been used for borehole stability, filtrate loss reduction, and enhancing the rheology of mud blends. Such materials are characterized by an extremely high surface area to volume ratio due to their nano-sized particles. Nanoparticles offer enormous characteristics to reduce frictional resistance between drilling pipes and side holes and optimize torque and drag due to their extraordinarily thin and fine structure. Furthermore, NPs have broad drilling capabilities in high pressure and high temperature (HPHT) environments due to their wider surface area [11, 12].

Numerous nanomaterials, including graphene oxide, graphene nanoplatelets, titanium oxide, aluminum oxide, cupric oxide, CNT, multi-walled carbon nanotube (MWCNT) nanosilica, clay, metals, and carbon-based NPs, have been used to enhance the performance of WBMs. It was observed that the mud containing nanoparticles possesses enhanced physical and chemical properties, which enhances its efficiency. Graphene nanoparticles were found to be an excellent binding agent because these can develop a compact, impermeable, and thinner mud cake. This allows nano-pores to be physically plugged, limiting filtrate losses. As a result, using the graphene family improves wellbore stability [13].

Additionally, nanoparticles have been introduced as lubricants to minimize friction between the wellbore and the drill string, lowering the risk of a stuck pipe. Figure 2 shows how nanoparticles have a higher surface area than macroparticles of the same volume.

Figure 2.

Comparison of nanoparticles surface area with bulk material.

In water-based mud systems, polymers nanoparticles such as TiO₂/PAM nanocomposite depicted reduced filtrate loss volume and filter cake thickness while enhancing the formulated mud’s rheology [14]. Likewise, SiO₂/acrylic nanocomposites showed improved thermal stability [15]. Numerous studies have concluded that the synthesized composites showed improvements in rheology and lubricity while a reduction was observed in the filtrate loss. Some of the common nanoparticles with potential applications in drilling fluids are summarized in Table 1.

Nanoparticles	Functions	Reference
TiO2-polyacrylamide hybrid	Reduced filtrate loss and improved mud viscosity	Sadeghalvaad and Sabbaghi [14]
CuO and ZnO	Improved viscosity at HPHT	William et al. [16]
Nanosilica	Filtrate prevention	Cai et al. [17], Fakoya and Shah [18]
Graphene oxide	Filtrate control agent in HPHT	Kosynkin et al. [19]
Nanosilica, multi-walled Carbon Nanotube	Improved rheology and filtration of mud, shale inhibition	Hoelscher et al. [20]
MWNT-polymer hybrid	Fluid loss reduction at HPHT conditions	Ito et al. [21]
Silica NPs	Filtrate reducer for drilling fluid at ultra-high temperature	Mao et al. [22]
Nano clay	Enhancing mud cake reduction	Zamir and Siddiqui [23]
Sepiolite NPs	Improving the rheological and filtration properties of mud	Al-Malki et al. [24]

Table 1.

Nanoparticle applications in drilling muds.

7. Field applications of high-performance WBMs

In response to increasing environmental restrictions and economic concerns, there has been an upsurge in demand for water-based muds (WBMs) in the last 15 years, particularly for off-shore operations. Industry operators and service providers demanded Water-based muds to substitute the stable and inhibitive invert emulsion fluids. Some of the most common problems with WBM are hole washouts, poor hole cleaning, bit balling, tight holes, inappropriate reaming and stuck pipe, shakers screens blockage, reducing total solids control equipment (SCE) performance, logging difficulties, and running casing are all associated with the appropriate mud design [25].

Numerous fields have applied HPWBMs to overcome the encountered problems, including complex formation drilling, high-temperature drilling, borehole instability, and high collapse stress formations. In China, the complex formations containing mudstone, fine sandstone, mudstone intercalated with salt rock, and pure salt rock were successfully drilled using HPWBMs. The mud exhibited better clay inhibition, rheological and filtration characteristics, and rate of penetration and was environmentally safe [26].

A well having issues during drilling including borehole instability, risk of induced losses, and tight hole owing to the presence of unstable shale was successfully drilled using HPWBM. The well was drilled to total depth without any NPT attributable to drilling fluid or hole cleaning. A gauge hole was drilled with minor washouts. The cuttings were distinct, suggesting good inhibition. In comparison to the fluid applied in former wells, the proposed HPWBM system demonstrated its superiority and efficiency [3].

Similarly, in South China’s deepwater well drilling operation, a high-efficiency mud system was determined to be acceptable, and the well application revealed that the selected mud is an excellent alternative to OBM or SBM [5]. HPWBM has been successfully deployed in different fields in Dubai, which contain higher reactive clays and have reached higher degrees of inclination [25].

A new HPWBM was designed to fill the gap between conventional WBM and emulsion-based mud systems in terms of drilling performance. The mud has been tested in the field with some of the most challenging onshore, deepwater, and continental shelf wells. These wells would otherwise have been drilled with oil or synthetic-based mud [27].

Scleroglucan as a mud additive has also been used during drilling of gas field exploration in various fields. The field experiments confirmed its salt and thermal stability and found a stable additive up to 80°C.

8. Limitations of biopolymers

Generally, the biopolymers have lower thermal stability and degrade at higher temperatures. The salts, calcium, and bacterial resistance also negatively impact the performance of the mud containing biopolymers. Thus other additives such as bactericides are added to prevent the bacterial attack. Owing to the reduced thermal stability, either the native materials are modified by adding more functionalized groups into their main chain or the addition of two or more biopolymers is used. The former is economical compared to the second one. In a study, the synergic effect of xanthan and diutan gum enhanced the performance of water-based drilling fluids and showed shear-thinning behavior [28].

Different researchers have attempted to modify the biopolymers for drilling fluid applications. Starch is one of the most widely used additives, which improves both rheology and the filtration behavior of the muds. Starches have been modified using chemical, physical and enzymatic approaches. The usage of starch in the petroleum industry is in the drilling fluids, enhanced oil recovery, and completion fluids. A variety of starches are available, which are generally used for food applications. Pregelatinized starch (PGS) has been used in the oil industry due to its lower costs. Carboxymethyl starches (CMSs) are also very common, showing better thermal stability and salt resistance in WBMs. The combination of polyanionic cellulose (PAC) with the modified starch shows significant improvements in terms of mud rheology and filtration. Acetylated and grafted starches also showed promising results in WBMs.

Acknowledgments

The authors would like to thank the Ministry of Higher Education (MOHE), Malaysia, for providing financial assistance under FRGS/1/2020/TK0/UTP/02/3.

Conflict of interest

The authors have no conflict of interest.

Nomenclature

HPWBMs	high-performance water-based mud
PAC	polyanionic cellulose
OBM	oil-based mud
SCE	solids control equipment
SBM	synthetic based mud
HPHT	high-pressure high temperature
NPs	nanoparticles
CNT	carbon nanotubes
PGS	pregelatinized starch
CMS	carboxymethyl starch
MWCNT	multi-walled carbon nanotube
ROP	rate of penetration