Maintaining Borehole Stability Research Articles

Application of ultra-fine particles of potato as eco-friendly green additives for drilling a borehole: A filtration, rheological and morphological evaluation

Drilling fluid is crucial for oil and gas well drilling operations, serving key functions such as facilitating the removal of drill cuttings, maintaining borehole stability and controlling formation pressures. When the drilling fluid is lost into formations, it can alter the formation's integrity, contaminate groundwater and cause permeability damage. In addition, environmental concerns arise from the waste produced during drilling activities, particularly when discarded drilling fluids contain hazardous substances like heavy metals. This study explores the potential of integrating ultrafine potato powder (PP) into water-based drilling fluids (WBDFs) as environmentally friendly additives. Several analytical techniques including X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electronic microscope (SEM) and differential scanning calorimetry (DSC) were used to comprehensively characterize the prepared PPs. The study included API and HPHT filtration test, permeability plugging test and rheological evaluations of drilling fluids, assessing parameters such as filter loss, filter cake, apparent viscosity, plastic viscosity, yield point and gel strength under varied conditions of different particle sizes of PP, concentrations of PP, and temperature and pressure measurements. The obtaining results emphasize PP's potential to enhance the wellbore stability and reduce the fluid loss, the filtration of water or oil into the permeable formation, achieving 43% reduction in the filtration rate and 70% reduction in the filter cake thickness. Adding 0.5 wt% ultrafine PP improved the maximum gel strength to 32.2 lb/100 ft2, while the same concentration and particle size raised the plastic viscosity from 3 to 6.8 cP, which subsequently dropped to 6 cP in high temperature conditions. PP performed better compared with the reference fluid in improving the thinning behavior of the drilling fluids. Moreover, permeability plugging tests confirm that adding PP effectively lowered the filtration rate, with higher concentrations achieving greater reductions over time. These findings suggest that PP holds promise as an effective additive for drilling fluids, contributing to enhanced drilling efficiency, improved wellbore stability and a reduced likelihood of instability and lost circulation. The characterization and rheological analysis of PP biodegradable drilling fluids provide valuable insights for optimizing fluid formulations, tailoring them to specific operational conditions, and achieving a balance between fluidity, wellbore stability, and cuttings transport. This research highlights the potential of PP as a sustainable and efficient solution in the realm of drilling fluid additives.

Borehole stability in naturally fractured rocks with drilling mud intrusion and associated fracture strength weakening: A coupled DFN-DEM approach

Borehole instability in naturally fractured rocks poses significant challenges to drilling. Drilling mud invades the surrounding formations through natural fractures under the difference between the wellbore pressure (Pw) and pore pressure (Pp) during drilling, which may cause wellbore instability. However, the weakening of fracture strength due to mud intrusion is not considered in most existing borehole stability analyses, which may yield significant errors and misleading predictions. In addition, only limited factors were analyzed, and the fracture distribution was oversimplified. In this paper, the impacts of mud intrusion and associated fracture strength weakening on borehole stability in fractured rocks under both isotropic and anisotropic stress states are investigated using a coupled DEM (distinct element method) and DFN (discrete fracture network) method. It provides estimates of the effect of fracture strength weakening, wellbore pressure, in situ stresses, and sealing efficiency on borehole stability. The results show that mud intrusion and weakening of fracture strength can damage the borehole. This is demonstrated by the large displacement around the borehole, shear displacement on natural fractures, and the generation of fracture at shear limit. Mud intrusion reduces the shear strength of the fracture surface and leads to shear failure, which explains that the increase in mud weight may worsen borehole stability during overbalanced drilling in fractured formations. A higher in situ stress anisotropy exerts a significant influence on the mechanism of shear failure distribution around the wellbore. Moreover, the effect of sealing natural fractures on maintaining borehole stability is verified in this study, and the increase in sealing efficiency reduces the radial invasion distance of drilling mud. This study provides a directly quantitative prediction method of borehole instability in naturally fractured formations, which can consider the discrete fracture network, mud intrusion, and associated weakening of fracture strength. The information provided by the numerical approach (e.g. displacement around the borehole, shear displacement on fracture, and fracture at shear limit) is helpful for managing wellbore stability and designing wellbore-strengthening operations.

Application of Hybrid Silicate as a Film-Forming Agent in High-Temperature Water-Based Drilling Fluids.

Effective control of shale swelling and lost circulation using drilling fluid is considered the dominant strategy for maintaining borehole stability, especially drilling operations in deep oil and gas wells. In this work, a hybrid silicate that contains lithium silicate and potassium methyl silicate (PMS) was employed as a film-forming additive to reduce shale hydration and filtration loss in the high-temperature drilling fluid. Scanning electron microscopy (SEM) results revealed that a dense quartz crystal film coating on the shale can be formed in a hybrid silicate solution when the temperature exceeds 150 °C. The in situ-formed film on the shale surface with a thickness of 60–130 μm was composed of fibrous crystalline silica. Furthermore, the aqueous hybrid silicate exhibited enhanced hydration inhibition ability by preventing water invasion of the formation. Aqueous hybrid silicate with a concentration of 0.5–3 wt % lithium silicate and 0.1–0.2 mol/L PMS was first chosen to obtain the optimum concentration according to the hydration inhibition ability and film formation characteristics. The hybrid silicate was added into a drilling fluid formulation applicable in high-pressure and high-temperature conditions, and the rheological characteristics and filtration properties were investigated. The results confirmed that drilling fluids with the addition of hybrid silicate can mitigate variation of viscosity and yield point before and after aging at 180 and 220 °C. Besides, the filtration behavior was also improved by adding hybrid silicate into the drilling fluid. A lower filtration loss was observed at the concentration of 1.0 wt % lithium silicate and 0.2 mol/L potassium methyl silicate, which showed 63 and 50% HPHT fluid loss reduction for unweighted and weighted formulations at 205 °C and 3.5 MPa, respectively. In addition, the drilling fluid featured stable rheological and filtration properties and excellent shale hydration inhibition characteristics when exposed to high temperatures, making it a promising candidate for drilling in deep oil and gas wells.

Influence of drilling fluid temperature on borehole shrinkage during drilling operation in cold regions

Frozen soil is a porous elastic-plastic-viscous material with temperature-sensitive properties. Borehole shrinkage occurs due to the plasticity and creep of frozen soil that ensues during drilling operations in cold regions. Based on the change of mechanical properties of frozen soil during the heat transfer process that occurs between the drilling fluid and the formation, a heat-fluid-solid coupling model is established in this paper to analyze borehole shrinkage behaviors in frozen soil. The results show that during drilling operations, the plastic and creep deformation of frozen soil will result in borehole shrinkage. When the borehole is drilled, a certain amount of plastic deformation will occur due to stress concentration. As drilling operations continue, both plastic and creep deformation gradually accumulate. The borehole shrinkage is dominated by the initial temperature of the formation, and the higher the formation temperature, the greater the shrinkage. At the same formation temperature, the initial borehole shrinkage decreases with increasing temperature of the drilling fluid, and the final shrinkage increases nonlinearly with increasing temperature. The drilling fluid temperature should be close to 0 °C when the formation temperature is high to reduce the drilling time. When the formation temperature is low, cold drilling fluid should be used to maintain borehole stability. This study provides a theoretical basis for the selection of drilling fluid temperatures during drilling operations in cold regions.

Numerical Study of a Flow Field Near the Bit for a Coiled-Tubing Partial Underbalanced Drilling Method

A new drilling method called coiled-tubing partial underbalanced drilling (CT-PUBD) was proposed in this paper. The method is not only able to enhance rate of penetration (ROP) just like the conventional underbalanced drilling technology but can also maintain borehole stability in the upper formation. In the new method, the wellbore pressure system is divided into two parts by a packer: (1) normal pressure system in the upper formation used to balance formation pressure and maintain borehole stability and (2) an underbalanced pressure system in the annulus near the bit used to enhance ROP. Because the pressure system and the circulation system are different, the cuttings transportation process of the method is different from the conventional way. Therefore, it is essential to study how to carry cuttings away efficiently. The flow field and cuttings distribution in the annulus near the bit were analyzed by computational fluid dynamic (CFD) methods. Cuttings transportation trajectory, velocity distribution, and cuttings concentration distribution were obtained under different holes’ parameters of the backflow device (including holes number, diameter, distance, and angle) and different drilling fluid viscosities. The results show that these parameters all have influence on cuttings carrying efficiency, and the most influential parameters are viscosity, angle, and diameter. According to the result of an orthogonal test, a suitable combination of the holes’ parameters was obtained. In the combination, the value of holes number, diameter, distance, and angle is 4, 50 mm, 300 mm, and 120 deg, respectively. This paper provides a theoretical basis for an optimization design of the new method.

Borehole Stability in Mudstone Shale and Coal Seams in the Daniudi Gas Field

In order to study the reasons for borehole instability, we calculated the mud density window for horizontal wells in complex formations based on logging data. From the results of the mud density window calculation, we found that for mudstone shales it decreases as the inclination angle and the azimuth increase, while for coal it took on negative values. We found that collapse and expansion are conducive to maintaining borehole stability, while in coal seams a positive mud density window can be achieved only by collapse (a decrease in the borehole diameter). It was determined that we need to increase the mud density from 1.2 to 1.4 g/cm3 and use drill pipes that are as small as possible for the longest possible period of time. In this case, the borehole trajectory should be determined according to the seam location and the mud density.

A wellbore stability analysis model with chemical-mechanical coupling for shale gas reservoirs

Chemical and mechanical coupling are the most important factors affecting wellbore instability. The main objective of this research is to propose a wellbore stability analysis model for shale gas reservoirs. A mathematical model was proposed to analyze wellbore stability based on a quantitative solution for stress induced by mechanical, hydraulic and chemical effects, and the effective stress tensor around the borehole in a cylindrical coordinate system was also obtained. Anisotropic mechanical properties and changes in the strength of shale rocks were collected from tri-axial compression experiments, direct shear tests and the literature. To examine for shear failure along the weak plane and across the weak plane, the effective stress tensor in a cylindrical coordinate system was transformed into the weak plane's local coordinate system and integrated into the strength criteria of the weak plane. In addition, the failure regions around a horizontal well were simulated at different drilling times and for different drilling directions, and the real causes of wellbore instability for well X201-H1 in the Sichuan basin were analyzed. The results indicate that the nonlinear evolution equation for the strength parameters obeyed the logistic model; the strength parameters decreased drastically as the soaking time increased over the first five days, after which the strength parameters decreased slowly. In addition, pore pressure increased and solute concentration decreased under the condition Cm < C0, while pore pressure decreased and solute concentration increased under the condition Cm > C0. The decrease in strength and the increase in pore pressure have significant impacts on the stability of wellbores within shale gas reservoirs. Pore pressure propagation changes the effective normal stress on the weak plane of the wellbore and results in the stress concentration exceeding the strength envelope. In traditional models, failure regions occur only on the surface of a borehole; however, in the new model, failure regions can also occur in the interior of a formation, and they can occur within four zones around a wellbore's circumference. The decrease of shale strength and the increase of pore pressure under the condition of water-based mud (WBM) has a greater impact than in oil-based mud (OBM), which help define the critical equivalent mud weight (CEMW) requirements at which the rate of collapse increases rapidly. To maintain borehole stability, a series of approaches must be adopted, including reasonable mud weight (MW), mud system, well path, physical plugging, etc. This model can be used to analyze the failure regions around boreholes and calculate the CEMW needed to maintain wellbore stability at different times. This model is different from, and more practical than, the traditional model.

The great potential of nanomaterials in drilling & drilling fluid applications

The continuous development of global economy with decreasing in available hydrocarbon sources and increasing discovery and extraction costs due to decrease in-situ oil and gas reservoir, displays the necessity of using new techniques for the improve rate of penetration and productivity in well. Nanotechnology has already contributed significantly to technological advances in the energy industries. Nanotechnology has the potential to introduce revolutionary change in drilling industry. Nanotechnology produces nanomaterials with many attractive properties, which can play an important role in intensifying mud cake quality, reducing friction, eliminating differential pipe sticking, maintaining borehole stability, protecting reservoir, and enhancing oil and gas recovery. Nano fluids can be designed by adding nano-sized particles in low volumetric fractions to a fluid. The nano particles modify the fluid properties, and suspensions of nano-sized particles can provide numerous advantages. This paper presents an extensive literature review of assessing the applications of nanomaterials in drilling and drilling fluids, and evaluates the potential technical benefits that these nanomaterials might provide to petroleum development and production.

Effect of Gas Hydrate Drilling Fluids Using Low Solid Phase Mud System in Plateau Permafrost

Designingand optimizing suitable drilling fluids for permafrost exploration to get gas hydrates at low temperature is one of most essential and urgent demands in the current research on exploration and exploitation of gas hydrates. The issue on rheological properties and maintaining borehole stability of drilling fluids is especially important to focus on. This work studies the gas hydrates and wellbore stability conditions and designs a low solid phase mud system with chemical additives. The measured values and effect on rheological and physical properties of the drilling fluids with different type and concentration of additives are studied. Hydration expansion is tested in laboratory to estimate the hydration property of different additives. It is showed that the drilling fluids with a dose of 1% HT have suitable rheological and physical properties at low temperature. Potassium ion performs well in preventing borehole instability and gas hydrate dissociation. According to the study, the optimized drilling fluid formula is: base mud + 10% NaCl + 5% KCl + 1 ‰ NaOH + 1% HT.

Application of Nanomaterials in the Fields of Drilling Fluids and Completion Fluids

Nanotechnology generates nanomaterials with many unique characteristics, which could play an active role in intensifying mud cake quality, raising cuttings removal ability, reducing friction, maintaining borehole stability, and improving the cementing quality. In this paper, a series of nanomaterials were introduced, and all of them had great influence on the properties of drilling fluids or completion fluids, which would be significantly important to wellbore stability, formation damage control, borehole cleaning, safety drilling, cementing quality, environmental protection, and the improvement of the progress and success rate of petroleum development and production. Finally, the further applications of nanomaterials in drilling fluids and completion fluids are also prospected.

Application of Nanomaterials in Reservoir Protection

Nanomaterials are of great importance to improving mudcake quality, reducing lost circulation, enhancing borehole stability, and protecting reservoir. Some nanomaterials, including nanometer plugging materials, nano-sized MMH drilling fluids, nanocomposite super-short fibers, water-based film-forming drilling fluids, nano-based drilling fluid, and so on, are introduced, and all of them have significantly influence on reservoir protection. As a result, the application of nanomaterials in the field of reservoir protection is very useful for maintaining borehole stability and protecting reservoir.

Study and Application of Nanomaterials in Drilling Fluids

Due to their special properties, nanomaterials had potential application value, and they could play an essential role in improving mudcake quality, assisting in film-forming, reducing lost circulation, and enhancing wellbore stability. Some nanomaterials, such as nanocomposite filtration-reducing agent, nanocomposite viscosifier, nanosized emulsion lubricant, nanometer organoclay, and so on, were introduced, and all of them had significantly influence on the process of drilling operations. As a result, the application of nanomaterials in the field of drilling fluids are very useful for cleaning borehole, maintaining borehole stability, protecting reservoir, and enhancing oil and gas recovery. Finally, the further application of nanomaterials in drilling fluids is also prospected.

Non-linear waves of fluid pressure and contaminant density in swelling shales

The control of drilling parameters, such as salt concentration, mud percentage and temperature is of fundamental importance for maintaining borehole stability when drilling through shale sections. For this purpose, a non-linear model of mechanic and chemo-poroelastic interactions between fluids, contaminants and solid matrix is presented. For the binary case we obtain a system of two non-linear coupled equations describing the isothermal evolution of fluid pressure and contaminant density in shales. In addition to the usual diffusive solutions obtained in linear analyses, a novel process is found. Indeed we show the presence of intense transient phenomena, i.e. quick non-linear shock waves of both pressure and contaminant. We apply this model first to a simple, homogeneous shale, then to more realistic cases, and finally to a non-compressive filter cake buildup. All these waves exhibit a Burgers solitary wave dynamics and can give destructive instabilities in deep drilling oil in shales.

Borehole stability in naturally fractured reservoirs during production tests

Based on the plane of weakness theory, a model for predicting borehole stability in fractured reservoirs under different stress states was estiblisted and the equations for solving borehole stability were developed. The minimum downhole pressures required to maintain borehole stability under different natural fracture occurrences were calculated by using the data from a well in the Tazhong (central Tarim) area, Tarim Basin, west China. Several conclusions were drawn for naturally fractured reservoirs with a dip angle from less than 10 ° to greater than 30 °. Application in three wells in the Tazhong area indicates that this model is practically useful.

Surface Casing Vent Flow And Gas Migration Remedial Elimination-New Technique Proves Economic And Highly Successful

Abstract Ever increasing pressure from environmental groups and government agencies has forced many operating and service companies to take a serious look at surface casing vent flows and gas migration. Concerns regarding well abandonment and lease reclamation, as well as aquifer contamination and green house gas emissions, have increased attention to the problem. This problem has plagued the oil and gas industry for many years. Experiments using various techniques to remedy it have been costly and have consistently had low rates of success. Wireline logging, high density perforating and cement/resin squeezing have been applied. The relevant gas zones usually have very low permeability and swelling clays, preventing feedrates with water. Consequently, cement squeezing is virtually impossible due to large cement particles bridging and hydrating immediately at the perforations; often no cement is squeezed into the formation. Furthermore, shallow formations may be fragile and can fracture under a hydrostatic cement column. Multiple gas sources, source locations, and misleading log interpretation have also contributed to poor success rates. A new technique is described here which is cost effective and meets regulatory and environmental requirements. It consists of formation evaluation and the application of abrasive hydro-jetting, hydraulic fracturing, and fine particle cement squeezing. Field results in southern and central Alberta show that the technique is highly successful; surface casing vent flows and gas migration have been terminated. Introduction Whenever a hole is drilled, there is the possibility that fluids previously trapped by impermeable layers will migrate to shallower zones or to surface. Unsuccessful primary cementing may leave voids and channels in the cement sheath, allowing fluids to migrate. As a result many wells leak gas to surface through soil gas migration and/or surface casing vent flows (Figure 1). In many areas of Alberta and Saskatchewan, the first 200 to 400 m of formation consists of gravel beds, silts, undeveloped shales with swelling clays, and "non-commercial" shallow gas bearing zones. These features make it difficult to maintain borehole stability and zonal hydraulic isolation. Gas can migrate through four possible passages: between the casing and cement (microannulus), through channels in the cement, between the borehole wall and cement, and through a permeable formation (Figure 2). A surface casing vent flow is any measurable flow of gas, water, or hydrocarbon liquids with or without pressure build-up(1). It is estimated that one out of 20 wells in Alberta has pressure on the surface casing vent. Gas migration refers to gas that migrates to surface through the soil outside the surface casing, around the wellbore. Husky Oil defines a "leaker" as any well with a detectable leak, including those with rates too small to measure with standard instrumentation. A successful remedial operation is one that stops all leakage for a year or more through at least one freeze-thaw cycle(2). Elimination of gas migration and surface casing vent flows has presented a considerable challenge to the oil and gas industry. In order to abandon a lease, government reclamation requires that the site be returned to its original state.

Environmentally Acceptable Water-Based Mud Can Prevent Shale Hydration and Maintain Borehole Stability

Summary This paper presents laboratory and field results showing that an environmentally acceptable water-based mud (WBM) can be formulated to act like an oil-based mud (OBM) in preventing hydration, pore-pressure increase, and weakening of shale by effectively developing sufficient osmotic force to offset the hydraulic forces acting to cause water flux into the shale. We also show that this methyl glucoside system has other performance characteristics similar to OBM's, such as lubricity, filtration control, and tolerance for common WBM contaminants, thus meeting the needs for drilling high-angle or even extended-reach wells.

Borehole-Stability Analysis for the Design of the First Horizontal Well Drilled in the U.K. Southern V Fields

Summary This paper presents the method and results of a borehole-stability analysis conducted on the first horizontal well successfully drilled in the North Valiant field in the Southern North Sea. Previous drilling data obtained from the same area were analyzed by numerical simulations of potential mechanical behavior of the wellbore. The magnitude of the in-situ horizontal stresses was determined by the analysis of fracture-stimulation data from wells in the fields. The directions of the stresses were derived from anelastic-strain-relaxation (ASR) measurements of fresh cores. Effects of hole azimuth on wellbore stability were evaluated. The analysis resulted in a design of optimum mud weights for maintaining borehole stability during drilling. This paper also discusses field results and well completions.