Water-based Mud Systems Research Articles

Application of Hydrothermal Synthesized Titanium Dioxide-Doped Multiwalled Carbon Nanotubes on Filtration Properties-Response Surface Methodology Study.

The success of any drilling activity mainly depends on the characteristics of the drilling fluid. Therefore, a high-performance drilling fluid is substantial for any drilling operation. During overbalance drilling operations, the drilling mud invades the permeable formations and causes the loss of circulation, which is responsible for nonproductive time events. Hence, the filtration characteristics of the drilling mud are an imperative property. The purpose of this study is to evaluate the filtration characteristics of water-based mud systems in the presence of polyanionic cellulose (PAC) and multiwalled carbon nanotubes (MWCNTs)/TiO2 nanoparticles. The nanoparticles were synthesized by using the hydrothermal technique. For the first time, a composite of MWCNTs and TiO2 has been utilized as a fluid loss control additive in the petroleum sector, marking a significant development in the field. The filtration properties of water-based mud were assessed at two concentrations (0.35 g and 3.5 g). Furthermore, based on the two levels (concentrations) and two factors (particles), the novel application of the central composite response surface design of experiment (CCD) was implemented. The results showed that the predicted model from CCD was in good agreement with the filter press experimental result with R 2 = 0.8446. Furthermore, based on the ANOVA analysis, the concentration of MWCNTs/TiO2 nanoparticles was the most significant parameter with p-value < 0.05. In addition, 10 out of 13 experimental points fall under the ±10% error window, thus indicating a higher accuracy of the regression model. The 2D interactive plots further show that the concentration of PAC is insignificant and has no considerable influence on fluid loss control, which was also validated by p-value > 0.05. The performance of MWCNTs/TiO2 nanoparticles is superior to PAC because these nanodimension particles plug the pore-spacing and block the permeation channels on the filter paper. However, the PAC, because of its long molecular chain, entangles around the pore spaces and plugs the microsize pores, which eventually reduces the filtration loss volume up to some extent. By observing the synergistic interaction between MWCNTs/TiO2 nanoparticles and PAC, this study develops valuable insights that assist in improving the performance of drilling fluid and minimizes the wellbore instability issues in the oil and gas sector.

Influence of triton-assisted coconut shell derived graphene nanoplatelets in water-based drilling fluid lubricity and shale inhibition application

Insufficient hole cleaning, cutting suspension, clay swelling, and filtrate invasion of the formation might result from inadequate drilling mud properties. For effective drilling and wellbore stability, water-based mud (WBM) rheology, lubricity, filtration, and shale inhibition must be optimized and controlled. WBMs react with clays and cause time-dependent borehole issues, which is their principal drawback. Moreover, prolonged exposure destroys certain WBM components, resulting in minimal mud properties. These indicate the need for multifunctional additives to improve WBMs. Thus, this study developed WBM systems employing graphene nanoplatelets (GNPs) and locally acquired discarded coconut shells to overcome severe drilling challenges. By adding triton-X100 to coconut shell-based graphene (GN-CS), a greater dispersion of modified graphene (GN-TX) particles was produced. Characterization, rheology, lubricity, inhibition, and filtration tests were performed on these GN-CS and GN-TX at concentrations of 0.125, 0.25, 0.375, and 0.50 wt%. Furthermore, biotoxicity, biodegradability, and heavy metal content experiments were performed to study the environmental impact of GN-CS and GN-TX. The results showed that GN-TX had good thermal resistance up to 300 °C with only a 10% loss in weight. Both EDX and FTIR tests showed that the epoxy, carboxyl, and hydroxyl groups are in the GNP-based materials' basal plane. The GN-CS and GN-TX had better fluid properties, including better lubricity, rheology, filtration, and inhibition over the base mud, and the optimal rheological model of the drilling muds was the Herschel Buckley model. The GN-TX (modified) decreased the fluid loss to 20.6–14.3 mL from 24.6 mL at 353 K, whereas the GN-CS (unmodified) reduced it to 21.3–16.7 mL. GN-TX and GN-CS decreased the coefficient of friction of WBM from 0.47 to 0.55 to 0.25–0.41 and 0.33–0.44, respectively, from 298 to 353 K. In addition, 0.50 wt% of GN-CS and GN-TX reduced the shale pellet swelling height to 5.4% and 5.6%, respectively, from 8.8%. Moreover, the EC50 values for GN-CS and GN-TX were about 54,000 mg/L and the BOD/COD ratio was about 47%. These results show that the GNP-based products are safe and biodegradable. The GNP-based materials have promising prospects for drilling in environmentally sensitive formations.

Investigation of silica coated iron oxide nanoparticles and activated carbon as a potential fluid loss additive and Pakistan shale inhibitor in water-based mud system coupled with advance image processing technique

Investigation of silica coated iron oxide nanoparticles and activated carbon as a potential fluid loss additive and Pakistan shale inhibitor in water-based mud system coupled with advance image processing technique

An Experimental Study to Assessing the Efficacy of Oil to Prevent Differential Stuck Pipe Incidents in Zubair Oil Field, Southern Iraq

This study focuses on the important role of drilling mud in successful drilling operations, particularly in preventing and treating differential stuck pipes. Differential pipe sticking (DSP) is a common challenge when drilling through a pay zone with water-based drilling mud containing bentonite clay. However, using oil as an additive in a water-based mud (WBM) system offers distinct advantages and can significantly improve drilling performance. The research utilizes the Fann VG meter, a self-fabricated tester, and a tester of stickance to investigate the impact of oil on water-based drilling mud (WBM) and controlling DSP to address this challenge. The empirical study demonstrates that adding oil to the drilling fluid enables it to maintain its rheological properties (PV, YP, and API fluid loss) while reducing filtration loss from 7 to 4.8 cc and friction coefficient from 0.30 to 0.05. This indicates that emulsion mud can mitigate the risks of differential sticking by maintaining the oil concentration within the recommended limit (not exceeding 3%). Balancing the maintenance of rheological properties with the reduction of friction coefficient is essential to reaching optimal drilling performance and preventing differential pipe sticking.

Application of graphene oxide/titanium dioxide nanoparticle on the rheological, filtration and shale swelling characteristics in water-based mud system: experimental and full factorial design study

Application of graphene oxide/titanium dioxide nanoparticle on the rheological, filtration and shale swelling characteristics in water-based mud system: experimental and full factorial design study

A Novel Approach Using Poly Amine and Copolymeric Sealants in Water-Based Mud Systems

A Novel Approach Using Poly Amine and Copolymeric Sealants in Water-Based Mud Systems

Innovative drilling fluid containing sand grafted with a cationic surfactant capable of drilling high pressure and high temperature geothermal and petroleum wells

Maintaining the rheology and filtration properties of a drilling fluid plays a vital role during a drilling operation. With the current challenges of high pressure and high temperature environments, there is an urgent need to design thermally stable water-based mud systems (WBM) which are environmentally clean and economically cheap.High pressure and high temperature (HPHT) environments affect drilling fluid systems leading to degradation of additives hence reducing the efficiency of the drilling fluid. Nanotechnology has been widely used to answer questions about additive degradation, and many studies are currently being conducted on how to use nanotechnology to design smart drilling fluids. However, nanotechnology comes at a high cost, resulting in an increase in the overall drilling operation costs and the project as a all. Therefore, the effectiveness of sand particles as a replacement of commercial nanoparticles is investigated in this study as an additive for designing effective-performance water-based drilling fluids. Effective-performance drilling fluids are environmentally friendly, stable at high temperatures, and help to avoid well damage during drilling operations.The research compared sand particles, which are widely available and inexpensive to silica nanoparticles at 0.5 wt% concentration. The samples were tested at different aging temperatures. Rheological properties were measured at room temperature up to 232 °C. The performance of sand and silica nanoparticles was studied by comparing each of the nanoparticle muds with the reference mud sample, taking filtration and rheological properties as the benchmark parameters. Experimental data showed that sand particles enhanced almost all the rheological and filtration properties of the WBM compared to the reference mud. When compared to silica nanoparticles, the results showed neither statistically significant variance in plastic viscosity and yield point among the samples, with muds containing sand particles performing similarly or better. Formulation S2 (35–70 μm) demonstrated the ability to improve the rheology of WBM. At 204 °C and 232 °C, Formulation S2 (35–70 μm) filtrate loss decreased by 16.35% and 29.52%, respectively, compared to 5.66% and 11.32% by mud containing nano silica. The same mud sample decreased the mud cake thickness at the same temperatures conditions by 54.74% and 45.45%, respectively, as opposed to 36.84% and 11.81%. The new innovative mud system can be used to drill in HPHT conditions.

Experimental Study on the Performance of Frictional Drag Reducer with Low Gravity Solids

Reducing energy consumption during drilling operations is beneficial to both the environment and economy. Frictional drag reducers (FDR) are widely used to reduce the energy loss caused by turbulent flow. FDR plays an important role in flow lines as they can reduce the frictional pressure drop effectively, and benefit the selection of circulating fluid and pump. However, several factors can influence the performance of FDR, including fluid additives and incorporated solids, such as drill solids. Thus, the main objective of this paper is to study the influence of low gravity solids (LGS) on the performance of the FDR. This paper is mainly based on experimental study. The experimental work contains two parts: rheology characterization and flow loop tests. Rheology characterization tests were performed to calculate the flow consistency index (K) and flow behavior index (n). Flow loop experiments were conducted for two geometry (0.457 inch and 0.797 inch diameter). Xanthan gum was used as a fractional drag reducer. Bentonite and quartz sand were added as low gravity solids. Three designed water-based mud systems are tested for drag reduction efficiency of Xanthan gum. Flow rate of the mud varied from 3 gpm to 16 gpm. Concentration of Xanthan ranged from 0.1 lbm/bbl to 0.6 lbm/bbl. Low weight solids were added with weight percentage of 0.5%, 1%, 2% and 2.5%. The result shows that xanthan gum is an efficient drag reducer for adequate reasons. Firstly, even at al low concentration, xanthan gum shows high resistance to degradation. Secondly, the maximum drag reduction with xanthan gum is up to 70.54% with a concentration of 0.6 lbm/bbl. However, the existence of different low gravity solids influence the efficiency of xanthan gum in different styles. Experiment results indicate that the higher the weight percentage of bentonite, the lower the drag reduction effectiveness. While with the increasing concentration of quartz sand, the drag reduction does not show an intense change. This study intents to give an instructive guidance on usage of frictional drag reducers in drilling mud system design. Removal of low gravity solids from the mud is difficult, which pose a danger to the drilling fluid. By understanding the effectiveness of FDR, we can reduce energy consumption when irremovable low gravity solids exist. FDR can be used for modifying the mud contents to develop a lower pressure gradient under turbulent flow condition. In the same scenario, adding FDR can suppress turbulent at a constant pressure gradient but with a higher flow rate.

Performance of Equilibrium Zeolite in Water-Based Mud at Elevated Temperature Conditions

This study looks at the performance of nano equilibrium zeolite treated drilling fluids at high temperatures conditions, and their potential as alternatives for oil-based muds (OBM). Mud samples for this study were prepared and aged with the equilibrium zeolite nanoparticles concentrations of 0.0 g, 0.5 g, 1.0 g and 1.5 g. Tests were performed to determine the rheological, filtration control properties, the pH and consequently the thermal stability of the study mud samples over a temperature range of 120 °F to 360 °F. One sample without the equilibrium zeolite served as a control for the study. From the results obtained, all the nano samples had their rheological properties not exhibiting much significant variation with temperature, thus they were more thermally stable, with the optimum nanoparticle concentration being 1.5 g. It was also hypothesized that the nano equilibrium zeolite behaved as thinners, since they were able to reduce the shear stresses, yield points, plastic viscosities and gel strengths of the mud samples as temperature was varied incrementally. It was therefore concluded that the optimum concentration of aged equilibrium zeolite has the potential to act as a thermal stability additive for Water Based Mud systems (WBMs).

Experimental evaluation of Sarcosine as an eco-friendly green hydrate inhibitor for the drilling of gas hydrate bearing formations

The hydrate inhibitors played a significant role in preventing hydrate formation in the drilling fluid systems. However, the disposal of these inhibitors was the primary concern for the drilling industries, as Thermodynamic Hydrate Inhibitors (THIs) are not eco-friendly, and Kinetic Hydrate Inhibitors (KHIs) are troublesome to dispose of due to their long polymeric structures. Hence, an attempt had been made to evaluate the Sarcosine, an amino acid, as a biodegradable, green hydrate inhibitor for water-based drilling fluid systems. Initial screening of Sarcosine in the THF-water hydrate (structure-II) system showed that it behaved as a zwitterionic, dual-function inhibitor. It had better inhibition characteristics in delaying induction time and improving rheological and filtration properties than PVCap and PVP while used in formulated mud compositions. The water-based mud used in this work was prepared by mixing carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), xanthan gum (XG), and potassium chloride (KCl) with distilled water. For Sarcosine content water-based mud systems, coefficients of determination (R2) values were dependable, while low-temperature (2 C) rheological values were fitted in Herschel-Bulkley model. These experimental investigations showed that the Sarcosine might be used for the drilling of gas hydrate-bearing formations.

Synthesis of Nanosilica and its application as Water Based Mud Rheology Enhancer

This study synthesized nanosilica from sodium silicate solution using precipitation method for 3:1 ammonia/ethanol ratio, and examines the effectiveness of the nanosilica in formulating high-performance water based mud system. Sodium silicate solution (SSS) is a low-cost precursor than tetraethyl orthosilicate. Three (3) solutions of sodium silicate with concentrations 0.5 N, 1 N and 1.5 N were used to precipitate nanosilica. The use of sodium silicate solution in alkaline medium produces less agglomerated nanosilica. The results gave Similarly, three (3) different samples of silica nanoparticles (Sample A, Sample B, and Sample C) with each concentration respectively. The silica nanoparticles from the Sample A had the smallest in size and quantity, and also the most dispersed. For Sample B, the nanosilica produced was apparently bigger than that of sample A in size and quantity produced. Sample C was produced using two procedures: Sample C1 (with ultra Sonicator) and Sample C2. (ultra Sonicator). Samples C1 and C2 produced the biggest size and quantity of nanosilica with less the dispersion. But, there were aggregation problems, due to the higher concentration of sodium silicate solution. There was no much difference between samples C1 and C2; just that with the former, the nanosilica was better dispersed and the latter was little more aggregated. The precipitated nanosilica, Sample B with 1 N concentration of SSS gave the optimum size and quantity, and was used to formulate the examined high-performance water based mud system. The silica nanoparticles had a positive effect on the drilling fluid systems flow properties. This due to their ultrafine size and high surface area. Also, nanosilica production is cheap and feasible, so it could easily replace other expensive additives.

Carbon Nanotubes as a Multifunctional additive and its Impact in Oil Based Mud System drilling Hydraulics

The drilling fluids should exhibit shear thinning characteristics to have less resistance at high shear rates. Nanoparticles can enhance the rheological properties of drilling fluids using different mechanisms. Nanomaterials are engineered materials with at least one dimension in the range of 1–100 nm. Carbon nanotubes were chosen in this study due to their unique physio-chemical properties, thus, a good candidate for smart oil based mud formulation. This study investigates the multifunctional ability of carbon nanotubes in oil based mud system and its impact on the drilling hydraulics. Application of carbon nanoparticles in literature have mostly been on water based mud systems and mostly at weight less than 2 g. Effect of carbon nanotubes on flow properties of oil based mud systems within the range of 1 to 3 g weight was analysed. The result shows that the carbon nanotubes improved the flow properties of the formulated oil based mud systems into an acceptable and desirable range required for optimal hole cleaning. The flow behaviour index (n) for the oil based mud systems for drilling hydraulics calculations were between zero and one, thus, they behaved like pseudo plastic fluids (Non-Newtonian fluids) both in the drill pipe and the annulus. It was also observed that, there was increase in the ratio of flow behaviour index to consistency index (n/K) and this will help reduce cuttings bed height in the wellbore.

A New Comparative Evaluation for the Rheological and Filtration Properties of Water-Based Drilling Fluids Utilizing Sodium Salt of Linear and Cross-Linked Acrylate Polymer Hydrogels

Currently, polymers were applied as the most functional additives for optimizing the rheological behavior and filtrate volume control of water-based drilling fluids. To affirm this concept, the present work aims to prepare sodium salt of linear polyacrylic acid (NaLPAA), polyacrylamide (NaLPAM) and their cross-linked polymer hydrogels (NaCPAA and NaCPAM), in different ratios using N,N′-methylenebis(acrylamide), as a cross-linker, potassium persulfate and ascorbic acid as initiators. FTIR characteristic spectra, 1H NMR analysis, SEM micrographs and elemental analysis for the formed gels were employed to emphasize their consistence. TGA and TGA-DTG thermo-grams displayed that NaCPAA polymer hydrogel offered the highest thermal stability behavior. The swelling behavior of the prepared hydrogels was examined and demonstrated that CPAM showed the best behavior at pH = 4 (acidic medium). The rheological properties of the investigated water-based mud samples were studied at various temperatures. For sample containing 0.57% (2 g) of NaCPAA at ambient temperature, it showed the highest rheological behavior in which AV achieved the highest value at 118 cP, PV was recorded at 69 cP, and YP was detected at 99 lbf/100 ft2. At LTLP conditions, sample containing 0.57% of XC-polymer and 2.86% bentonite in its composition offered the most enhanced mud cake thickness at 4.2 mm. At HTHP conditions, the filtrate volume of sample containing 0.29% NaLPAA was detected at 35 mL and for sample containing 0.57% was calculated at 22 mL. In addition, the modified mud samples with the same recipe of NaLPAA and NaCPAA at different applied temperatures showed moderate rheological properties compared to the commercial XC-Polymer. Furthermore, NaCPAA manifested a reduction in the swelling properties of water-based mud system containing high amount of API bentonite (2.85%, 10 g) in which AV and PV were calculated at 30 and 17 cP, respectively. In addition, YP was recorded at 22 lbf/100ft2. So, it could be used as a thinner for water-based bentonite mud systems.

Rheological study of fluid flow model through computational flow dynamics analysis and its implications in mud hydraulics

Oil and Gas drilling is not a simple fundamental procedure, never the less it accounts many subsurface uncertainties to deal with. The primary objective of an efficient and optimized drilling program is to analyze the formation uncertainties and chose a systematic logical approach for pursue drilling operations to overcome any problem encountered. Wellbore stability is the most important and cardinal part of drilling i.e. 1. Maintaining wellbore stability limits the Non Productive Time (NPT) for a well and 2. Analyzing the GTO to select a logical and effective approach for drilling saves time and allows remedial measures to get prepared for instability if encountered. During the process of drilling, the stability of wellbore is achieved by minimizing the fractures across the wellbore, which will occur mainly due to imbalanced mechanical forces. If the stresses acting on the wellbore surfaces increases then there will be a chance of pipe stuck due to formation collapse, which makes the wellbore cleaning difficult. The present paper deals in accordance with developing an understanding of the problems associated with wellbore instabilities and focuses on designing of proper drilling fluids formulations to counter these problems. The major experiments conducted are for analysis of formulating mud, namely: a. KCL-Polymer mud system b. Salt saturated mud system. Designing of drilling fluid done for Water Based Mud Systems only using additives in different proportions to maximize control and ensure cost effectiveness of the mud. Apart from the above oil well cleaning has been approached by the Navier stoke’s equation, power model, continuity equation to develop a mathematical model to help us understand the lifting of the cuttings as a function of fluid viscosity, density, fluid velocity. This in turn helps us to generate the flow regimes near the wellbore around the tubing while transporting the cuttings. The phase of CFD analyses has initiated with the motto of understanding the flow models and verifying the graphs generated from the simulation on the conventional Software’s.

Determining the Optimum Concentration of Pumpkin Seed Shells as Filtration Control Additive to Water-Based Mud System

Filtrate loss within formations is one of the biggest problems during drilling operations. Therefore, many commercial chemical additives have been used to reduce fluid loss, such as carboxymethylcellulose (CMC) and polyanionic cellulose (PAC), which are expensive and are not environment-friendly substances. This study evaluates the usage of pumpkin seed shells (PSS), which is agricultural waste and at the same time an environment-friendly material, as an additive to the drilling fluid to reduce fluid loss. Six drilling fluid samples were formulated, adding PSS of 250 μm in size at different concentrations (1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%). The effect of adding PSS on rheological properties and density was recorded and analyzed. Filtration was also studied by using an API LT LP press. The results of the study indicated that the addition of PSS to the drilling fluid has a clear effect on reducing fluid loss. The optimum concentration of PSS was 5 wt%.

Synergistic application of polypropylene and silica nanoparticle modified by (3-Aminopropyl) triethoxysilane for cuttings transport

Achieving the desired efficiency in cuttings transport has always been a challenge during drilling situations due to complex wellbore trajectories and drilling hydraulics. These issues require suitable additives to formulate the drilling muds. Hence, nanocomposite (NC) particles formed from silica and polypropylene was modified by (3-Aminopropyl) triethoxysilane (termed PP-SiO2 NC-NH2) and the impact of the concentrations of the PP-SiO2 NC-NH2 between 0.4 and 1.2 ppb on the cuttings transport efficiency (CTE) of complex water-based mud (WBM) system was assessed. Mud system containing 0.5 ppb PP-SiO2 NC-NH2 on CTE was measured and compared with that of partially hydrolyzed polyacrylamide (PHPA) using sandstone grains of diameters between 0.50 and 3.20 mm at hole angles 0, 30, 45, 60, and 90° with a 42 L/min pump rate. The zeta potential (ζ-potential), particle size distribution, morphology, and temperature resistance of the NC were examined. The ζ-potential data revealed the stability and the long-term stabilization of the modified NC in drilling muds. By adding the concentration of the modified NC into the WBM system, the thinning characteristics and consistency factors were enhanced as the NC concentration increases. Furthermore, the rheological test program reveals that the NC concentrations and 0.5 ppb PHPA increased the shear stress of the WBM with an increase in the shear rate. However, the mud system of PHPA exhibited a larger viscosity, while the NC samples showed a flat viscosity-profile. Also, the NC demonstrated better cuttings recovery than the PHPA product at 0.5 ppb concentration, especially at the worst hole angle of 45°. The cuttings recovery from a minimum to a maximum was found to occur in this order; 45°, 60°, 30°, 90°, and 0°. In contrast with the smallest and intermediate sand grains, the largest grains have complex and less fluid transport. With a pipe orbital motion of 150 rpm and a pump rate of 42 L/min, the CTE of the muds showed higher improvement. Overall, the mud properties of the modified NC exhibited a strong enhancing impact on the cuttings carrying capacity of the base mud than the PHPA.

Assessing the impact of an ionic liquid on NaCl/KCl/polymer water-based mud (WBM) for drilling gas hydrate-bearing sediments

Herein, 1-methyl-3-octylimidazolium tetrafluoroborate (OMIM-BF4) was tested as a potential additive to enhance the rheological and hydrate inhibition properties of polymer water-based muds (WBMs) for drilling natural gas hydrate sediments. API standards were adopted for the mud testing with and without OMIM-BF4, while the hydrate study was conducted using a high-pressure reactor at 8 MPa and −2 °C. The presence of OMIM-BF4 efficiently improved the rheological properties of the PAC and XGUM based muds by decreasing their flow behavior index by 4.97% and 47.77% and increasing their consistency index by 96.00% and 33.63%, respectively. The XGUM based mud system exhibited efficient rheological properties suitable for drilling hydrate reservoir compared with the PAC based mud system with and without OMIM-BF4. The Hershel-Bulkley model best predicted the rheological properties of all the mud systems by exhibiting less Mean Percentage Error (MPE) values in the range of 1.39% – 24.71%. Furthermore, the presence of OMIM-BF4 greatly inhibited methane hydrate formation in both PAC and XGUM water-based mud systems due to its kinetic inhibition efficiency mainly arising from its long alkyl chain hydrophobic adsorption activity on the hydrate crystals.

Improving the performance of oil based mud and water based mud in a high temperature hole using nanosilica nanoparticles

Oil-based mud (OBM), a non-Newtonian fluid, is known for its superior performance in drilling complex wells as well as combating potential drilling complications. However, the good performance may degrade under certain circumstances especially because of the impact of chemical instability at an elevated temperature. The same phenomenon occurs for water-based mud (WBM) when it is used in drilling under high temperature conditions. To prevent this degradation from occurring, numerous studies on utilizing nanoparticles to formulate smart fluids for drilling operations are being conducted worldwide. Hence, this study aims to evaluate the performance of nanosilica (NS) as a fluid loss reducer and a rheological property improver in both OBM and WBM systems at high temperature conditions. This study focuses on the impacts of different nanosilica concentrations, varying from 0.5 ppb to 1.5 ppb, and different mud weights of 9 ppg and 12 pg as well as different aging temperatures, ranging from ambient temperature to 300 °F, on the rheological performance of OBM and WBM. All the rheological properties are measured at ambient temperature, and additionally tests, including lubricity, electrical stability, and high-pressure high-temperature filtration measurements, are conducted, and rheological models are obtained. The performance of nanosilica is then studied by comparing each of the nanosilica-enhanced mud systems with the corresponding basic mud system, taking the fluid loss and rheological properties as the benchmark parameters. Nanosilica shows a positive impact on OBM and WBM, as the presence of nanosilica in the mud systems can effectively improve almost all their rheological properties.

An Adaptable Water-Based Mud System for Multiple Applications While Drilling

Due to significant variations of the subsurface geology from the surface to the top of reservoir and requirement of different fluid characteristics for drilling various hole there is a need to use various mud systems. These may include a simple spud mud for surface hole section, an inhibitive drilling fluid for reactive shale section, a salt water-based mud for salt diapirs and salt formations, and a highly lubricating mud for deviated hole sections with high dogleg severity.To optimize each of these separate and distinct scenarios, there is a need to change the mud system while drilling to overcome the technical challenges associated with these formations and wellbore profiles. The change over from one mud system to another is typically done between casing points while constructing the well to overcome specific drilling challenges associated with next whole section.There is significant time and effort required to clean the mud circulation system adequately before a mud change over in order to avoid any contamination of the new mud system.This is especially true when displacing a waterbased mud by an oil-based mud or an oil-based mud by a water-based mud.If this is not done properly, contamination of the new mud by the old mud could be a source of major problems due to partial or complete loss of functional ability of the new mud system. An adaptable drilling mud system that can easily be transformed from a spud mud system to an inhibitive, or a high lubricating or a salt water mud can provide the industry a versatile fluid system with multiple hole section applications.This removes much of the NPT associated with mud changeover, reduces the mud cost as compared to mixing a totally new mud system and eliminates concerns regarding mud contamination as well as any disposal or recycling cost for the replaced system. This paper describes a volcanic ash-based drilling mud that can be used as a spud mud to drill the surface hole, can easily be converted to an inhibitive mud system to drill reactive shale sections of a borehole, a salt water-based mud to drill the salt sections and also a high lubricating water-based drilling mud to reduce torque and drag problems in deviated and horizontal boreholes. The flexible and easily convertible nature of the base volcanic ash-based drilling mud has potential to reduce total drilling cost significantly as it eliminates a significant portion of non-productive drilling time associated with mud changeover, cleaning of mud circulation system, new mud preparation, incorporation of new mud in the circulation system and displacement of the old mud from the borehole by the new mud, etc.

Improved Wellbore Stability in North Sea Lark and Horda Shales Through Shale/Fluid-Compatibility Optimization

Summary Offshore wells drilled in the central and northern North Sea have historically suffered from borehole-instability problems when intersecting the Upper/Lower Lark and Horda Shale formations using either water-based mud (WBM) or oil-based mud (OBM). A wellbore-stability investigation was performed that focused primarily on improving shale/fluid compatibility. It was augmented by a look-back analysis of historical drilling operations to help identify practical solutions to the borehole-instability problems. An experimental rock-mechanics and shale/fluid-compatibility investigation was performed featuring X-ray-diffraction (XRD) and cation-exchange-capacity (CEC) characterizations, shale accretion, cuttings dispersion, mud-pressure transmission, and a new type of borehole-collapse test for 10 different mud systems [WBM, OBM, and high-performance WBM (HP-WBM)]. The results of this investigation were then combined with the results of a well look-back study. The integrated study clearly identified the root cause(s) of historical well problems and highlighted practical solutions that were subsequently implemented in the field. The borehole-instability problems in the Lark and Horda Shales have a characteristic time dependency, with wellbore cavings occurring after 3 to 5 days of openhole time. The problems were not related to mud-weight selection but were instead caused by mud-pressure invasion into the shales, which destabilizes them over time. An experimental testing program revealed that this effect occurs in both WBM and OBM to an equal extent, which explains why nonoptimal field performance has historically been obtained with both types of mud systems. New HP-WBM formulations were identified that improve upon the mud-pressure invasion and borehole-collapse behavior of conventional OBM and WBM systems, yielding extended openhole time that allows the hole sections in the Lark and Horda Shales to be drilled, cased, and cemented without triggering large-scale instability. Look-back analysis also indicated that secondary causes of wellbore instability, such as barite sag, backreaming, and associated drillstring vibrations, should be minimized for optimal drilling performance. A new HP-WBM system, together with improved operational guidelines, was successfully implemented in the field, and the results are reported here.