Optimal Synthesis, Characterization, and Performance Evaluation of High-Pressure High-Temperature Polymer-Based Drilling Fluid: The Effect of Viscoelasticity on Cutting Transport, Filtration Loss, and Lubricity

Abstract

Summary Viscoelasticity plays a significant role in improving the performance of the drilling fluid by manipulating its elastic properties. An appropriate value of the first normal stress difference (N1), extensional viscosity (ηe), and relaxation time (θ) enhance the cutting transportability, hole-cleaning ability, filtration loss, and lubrication behavior. However, the performance of the drilling fluid deteriorates during the drilling of high-pressure and high-temperature (HPHT) wells under acid gas and salt(s) contamination. Therefore, it is a challenging task to synthesize a thermally and rheologically stable drilling fluid, which is acid as well as salt(s) resistant, and maintain its desired properties. Although several water-soluble synthetic polymer-based drilling fluids have been used widely for the drilling of HPHT wells, most of these are limited at less than 200°C. Polyanionic cellulose (PAC) has an excellent heat-resistant stability, salt tolerance, calcium and magnesium resistant, and strong antibacterial activity, and it exhibits exceptional filtration and rheological behavior under HPHT conditions. However, using PAC beyond 200°C is limited because of the presence of the biodegradable cellulose units in it. To use the extraordinary properties of PAC, it is aimed to increase the thermal stability of PAC through appropriate modification. In this study, PAC-grafted copolymers involving acrylamide (a salt-tolerant viscosifying agent), 2-acrylamide-2-methyl-1-propane sulfonic acid (a thermally stable lubricating and fluid-loss control agent), and sodium 4-styrene sulfonate (a high-temperature deflocculant) is synthesized optimally through maximizing the thermal degradation stability of the grafted copolymer and minimizing the filtration loss as well as the coefficient of friction (CoF) of the drilling fluid simultaneously. Optimally synthesized PAC-grafted copolymers are then used to prepare water-based mud (WBM) involving American Petroleum Institute (API)-grade bentonite and alpha-glycol functionalized nano fly ash, and the tests for steady shear viscosity and viscoelasticity are performed to determine the rheological stability of mud beyond 200°C. The amplitude sweep tests for viscoelasticity are performed to determine the linear viscoelasticity range (LVR), structural stability, gel strength, and dynamic yield point (YP), whereas frequency, time, and temperature sweep tests are performed to obtain the elastic modulus (G′), viscous modulus (G″), and complex viscosity under HPHT conditions to check the stability of the drilling fluids under different holding times. Dynamic and static aging tests of the developed drilling fluids are performed at elevated temperature and pressure, and the aged muds are tested by evaluating the rheology, frictional, and filtration-loss behavior as per the API recommended procedure. The stability of the aged muds is also tested by evaluating the N1, ηe, and θ using a cone and plate rheometer. The performance of the proposed drilling fluids is also tested under acidic, sodium chloride (NaCl), and calcium chloride (CaCl2) environments at HPHT bottomhole conditions. The experimental results under HPHT conditions reveal that the performance of the mud (i.e., thermal stability, cutting transportability, hole-cleaning ability, filtration loss, and lubrication behavior) could be considerably improved by increasing the elastic properties of the drilling fluid by manipulating the molecular weight of the proposed PAC-grafted copolymer. Finally, the environmental effect of the developed muds is evaluated by finding the lethal concentration that kills 50% of the shrimp population (i.e., LC50) and the Hg and Cd contamination, and they are found to be environmentally safe.

NovelN,N‐dimethylacrylamidecopolymer containing multiple rigid comonomers as a filtrate reducer inwater‐baseddrilling fluids and mechanism study

“…The stretching band at 1363.96 cm −1 originates from CNC of the imide in the NVP unit 28 . Then, bands at 1183.21 and 1038.26 cm −1 arise from the SO stretching vibration of the sulfonic group in the SSS and AMPS units, respectively 34,46 …”

“…Recently, sodium 4‐styrenesulfonate (SSS) monomer has attracted extensive attention due to its good thermal stability, strong hydration properties, and great potential in the development of high‐temperature‐resistant drilling fluid in the petroleum industry. Gautam and Guria used polyanionic cellulose (PAC), AM, AMPS, and SSS to synthesize a PAC‐grafted copolymer, which, according to reports, can control drilling fluid filtration and perform excellent rheological properties even after aging at temperature as high as 225°C 34 . Synthesized by Huang et al, the rheology modifier and fluid loss additive (AADS) with AM, AMPS, SSS, and dimethyl diallyl ammonium chloride monomers was showed by experimental results that the AADS was capable of withstanding 240°C in a WBDFs with 4 wt% NaCl 35 .…”

Zwitterionic Silica-Based Hybrid Nanoparticles for Filtration Control in Oil Drilling Conditions

“…Well stability is one of the most troublesome issues that should be solved for oil and gas well drilling. Addressing the well instability of increasingly complex geological conditions and emerging ultradeep well over 8000 and 10,000 m remains challenging. − Chemicals in drilling fluids may undergo thermal degradation, cross-linking, desorption, water absorption, and other damages, leading to filtration loss and uncontrolled rheological performance. These phenomena are prone to occur in water-based drilling fluids (WBDFs), , which aggravate the instability of a borehole wall.…”

Nanomaterial-Based Drilling Fluids for Exploitation of Unconventional Reservoirs: A Review

“…Recently, researchers have widely studied polymeric material in conjunction with bentonite to prepare drilling fluids for harsh condition, in particular HPHT [33,34]. Molecules of polymer have long carbon chains and yield viscosity in the solution form [32,35]; thus, influencing rheology filtrate loss and lubricity of drilling fluid systems [31,36].…”

“…Nanosize additives with enhanced characteristics are actively being investigated in regards to drilling of HPHT wells [33,50]. Several nanomaterial have been investigated such as nano silica [51], graphene oxide [52], graphene nanoplatelets [43,53], multi-walled carbon nanotube [51,54,55], single walled carbon nanotube [54,56], nano ZnO [57,58], TiO 2 [59], CuO [60], and Fe 2 O 3 , nano-cellulose, nano-silica polymer grafted polymer [61], ZnO polymer nanocomposite [43], TiO 2 /polymer nanocomposite [62], TiO 2 /clay nanocomposite [63], and several others [64].…”