Non-aqueous Drilling Fluids Research Articles

Mud-to-cement conversion of non-aqueous drilling fluids using alkali-activated fly ash

Driven by the needs for reduced waste disposal and a sustainable environment, many efforts have been made to recycle coal combustion products. Fly ash, for instance, has been well-researched and successfully re-used in various industries and fields. Despite the potential for various applications, only 1% of the recycled fly ash has been directed to the oil and gas industry. The present study evaluated the feasibility of using alkali-activated fly ash (AAF) as an alternative cementitious material in well cementing applications.The key finding of this study is that AAF slurries provide improved compatibility with oil-based and synthetic-based drilling muds (OBM/SBM) in comparison to Portland cement slurries. Benefits of using AAF go beyond mere OBM/SBM compatibility: it is in fact possible to incorporate large amount of non-aqueous drilling fluids (NAF) such as SBM and OBM into AAF formulations while maintaining necessary well cement characteristics. This also means that NAF-associated waste can be disposed of in a more cost-effective way, which presents a viable option for environmentally acceptable on-site or off-site disposal of drilling muds and cuttings.In the present work, a novel mud-to-cement conversion method was achieved by blending varied amounts of AAF and SBM. The consolidated AAF/mud mixture was named “AAF hybrid cement”. In an effort to develop the AAF hybrid system as a novel well cementing material, fresh state properties, such as slurry rheology and thickening time, and hardened state mechanical properties, such as compressive strength, were comprehensively studied. The laboratory evaluations showed that the AAF hybrid cement could meet the typical characteristics and requirements of a well cementing slurry. By changing the relative amount of AAF and SBM in the slurry, the AAF hybrid can be deliberately designed with high compressive strength for primary cementation, or with lower compressive strength for lost circulation control.

Technology Focus: Cementing and Zonal Isolation (May 2019)

Technology Focus Cementing and zonal isolation are critical through the life cycle of the well. As I read through the cementing papers that were presented this year, I observed discussions on cementing and zonal isolation during drilling, completion, and abandonment activities. I am encouraged that we, as an industry, continue to refine and tweak our practices to solve zonal-isolation and cementing challenges in every well environment in which we work. Numerous papers not included here target improving cementing applications. Discussions about the mitigation of losses, low-density slurries, foam-cement slurries, spacer design, centralizer programs, expanding agents, flexible cement, and the management of narrow pressure margins are spread throughout SPE conferences. As cementing techniques are improved, so, too, are the cement-evaluation methods and work flows. The proof of zonal isolation is important to many, including resource owners, operators, regulators, land owners, and other stakeholders. As we drill longer extended-reach and horizontal wells, we continue the quest for zonal isolation using new technologies. Paper SPE 191561 discusses the mitigation of mud channels in horizontal wells drilled with nonaqueous drilling fluids. Academia has been experimenting and investigating placement practices. Recommended additional reading paper SPE 191989 explores the balance of buoyancy and eccentricity in both regular and irregular geometries. Another technology that is becoming more prevalent is the use of managed-pressure drilling, which leads to the need to understand managed-pressure cementing (MPC). Recommended additional reading paper SPE 191344 provides a case study for the use of MPC in both riserless mud recovery and con-trolled mud level applications. Abandonment is the final zonal-isolation activity in the well life cycle. The application of alternate materials continues to be discussed in all of our conferences. Paper SPE 193118 demonstrates the use of bismuth and thermite as an abandonment material. Paper SPE 191607 discusses the activation (and proof) of shales for zonal isolation. And finally, recommended additional reading paper SPE 191335 provides insight into the ultimate objective of cement-plug integrity. Recommended additional reading at OnePetro: www.onepetro.org . SPE 191989 Displacement Efficiency for Primary Cementing of Washout Sections in Highly Deviated Wells by Alondra Renteria, University of British Columbia, et al. SPE 191335 Cement Plug Hydraulic Integrity—The Ultimate Objective of Cement Plug Integrity by Axel-Pierre Bois, CURISTEC, et al. SPE 191344 Experience Using Managed-Pressure Cementing Techniques With Riserless Mud Recovery and Controlled Mud Level in the Barents Sea by E. Claudey, Enhanced Drilling, et al. SPE 193965 Caprock Restoration in Well Abandonment: Fit-for-Purpose Well-Abandonment Design Through Work Flow Optimization and Integrated Assessment by Jing Zhi Kueh, Petronas, et al.

Model Simulates Gas Kicks in Nonaqueous Drilling Fluids

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 189606, “Gas Kicks in Nonaqueous Drilling Fluids: A Well-Control Challenge,” by Z. Ma, A. Karimi Vajargah, D. Chen, and E. Van Oort, SPE, The University of Texas at Austin, and R. May, J.D. MacPherson, SPE, G. Becker, SPE, and D. Curry, SPE, Baker Hughes, a GE Company, prepared for the 2018 IADC/SPE Drilling Conference and Exhibition, Fort Worth, Texas, USA, 6–8 March. The paper has not been peer reviewed. Nonaqueous drilling fluids, such as synthetic-based and oil-based mud (SBM and OBM, respectively), are used frequently to drill one or more sections of a well to reduce drilling problems such as shale sloughing, wellbore stability, and stuck pipe. However, solubility of formation gas in such fluids makes early gas detection, and the well-control process, very challenging. This is of particular concern in deep offshore wells. This paper presents a novel and comprehensive hydraulic model to simulate a gas kick in nonaqueous drilling fluids. Introduction Early kick detection becomes cumbersome when a nonaqueous drilling fluid is used. This is because of dissolution of gas in the nonpolar base fluid. Although gas entrance into the well still will result in increased flow-out on surface, the flow signature will be less pronounced in comparison with a similar gas kick in water-based mud (WBM). Moreover, the emergence of gas from the solution may often only begin when the gas/drilling-fluid mixture is relatively close to the surface, which leaves the crew only a short period to react before gas reaches the surface. Constant-bottomhole-pressure/managed-pressure drilling (CBHP-MPD) offers the benefit of delaying the bubblepoint until the kick has passed the choke, thereby not allowing the kick to come out of solution in the actual well. Background Gas-Kick-Simulation Multiphase-Flow Modeling. The drift-flux model (DFM) used in this work is a mechanistic model consisting of separate mass-balance equations and a combined momentum-balance equation, together with several closure algebraic equations and a slip law. To obtain the velocity of each phase, the slip law is used in conjunction with the combined momentum-balance equation. Solubility in oil-based drilling fluids is directly proportional to pressure, gas specific gravity, and base-oil volume in the drilling fluid and is inversely proportional to temperature, drilling-fluid solids content, and brine and emulsifier volumes in the drilling fluid. For a given drilling-fluid volume, the relative volumes of base oil, brine, and emulsifier in the drilling fluid can be determined from a standard retort analysis. However, the most-reliable method to determine this crucial simulation parameter is to conduct pressure/volume/temperature (PVT) testing for each mixture under downhole conditions. DFM Formulation. Mathematical modeling of a proposed 1D DFM to describe the multiphase-flow dynamics for non-aqueous drilling fluids is discussed in detail in the complete paper. The current formulation takes into account the mass transfer between the liquid (drilling fluid) and formation/injected gas. The model consists of two sets of partial differential equations for two different cases: when gas is completely dissolved in the liquid (no free gas) and when dissolved and free gas coexist in the system.

Cellulosic Cyperus esculentus L. as a filtrate loss modifier in field applicable aqueous and non-aqueous drilling fluids

The design and formulation of drilling fluids require additives that are cost-effective and environmental friendly in line with international best practices. This study was conducted to investigate the potentials and effects of Cyperus esculentus (Tiger Nut) as a filtrate loss modifier in field applicable aqueous and non-aqueous drilling fluids. Sixteen (eight aqueous and eight non-aqueous) drilling fluid systems were formulated, four aqueous and non-aqueous had Cyperus esculentus as a filtration additive, while the others do not contain the additive. The rheological properties, as well as the fluid filtration properties of the drilling muds, were investigated and compared with standard drilling mud. To ascertain validity, the results obtained were validated with the classic filtration model to ensure fit. Results obtained showed that the formulated mud systems had rheological properties that favored the suspension and transportation of drill cuttings, as well as the prevention of flocculation and clogging of drill strings. The rheological properties also showed a progressive trend as the concentrations of the additive were increased from 2 to 8 ppb. It was also further observed from the API and HPHT filter press test that the increase in the concentration of the additive exhibits a progressive trend that can be compared with the standard. In addition, it was observed from the classic filtration model that the experimental results from both mud systems were fit for the adopted model.

Modified Rectorite Provides Reliable Rheology and Suspendability in Biodiesel-Based Fluids

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 189310, “Novel Modified Rectorite Provides Reliable Rheology and Suspendability for Biodiesel-Based Drilling Fluid,” by Wai Li, SPE, Beijing Oilchemleader Science and Technology Development Company; Jishan Liu, The University of Western Australia; Xionghu Zhao, Jian Zhang, and Jiwei Jiang, SPE, China University of Petroleum; Tao He, GWDC Drilling Fluid Company; Liu Liu and Peiyuan Shen, The University of Western Australia; and Min Zhang, Sinopec, prepared for the 2018 SPE/IADC Middle East Drilling Technology Conference and Exhibition, Abu Dhabi, 29–31 January. The paper has not been peer reviewed. The use of organophilic clays as additives to provide proper rheological and filtration properties in nonaqueous drilling fluids (NADFs) has long been a topic of study. Currently, most of these clays are based on the modification of bentonite with quaternary ammonium salts. As new NADF systems emerge, novel clay-modification technologies are needed to obtain more-effective organophilic clays for specific drilling fluids. This paper introduced a modified rectorite designed for biodiesel-based drilling fluid (BBDF). Introduction Biodiesel has drawn a great deal of attention from petroleum scientists and drilling engineers who are seeking environmentally friendly, high-performance, low-cost drilling fluids. The advantageous properties of biodiesel—such as a high flash point (for fire safety), sufficient viscosity (to carry cuttings to the surface during drilling), low eco-toxicity, excellent biodegradability, and good lubricity—make it suitable as a base oil for drilling fluid. Biodiesel also is relatively inexpensive in many situations. Many investigations and trials are being con-ducted on BBDF, suggesting some exciting results. A general necessity for new drilling-fluid techniques is to customize a series of corresponding chemical additives; BBDF is no exception. Preliminary experience has shown that an additive used in traditional oil-based drilling fluids (OBDFs) may be unable to perform well in a BBDF system. Consequently, new additives should be developed for BBDF in order to obtain the optimal operational and environmental properties. Traditionally, most organophilic clays for drilling fluids are based on the intercalating reaction between bentonite and quaternary ammonium salts, which are classified as cationic surfactants. However, this type of organobentonite (OB) still has some disadvantages, such as eco- toxicity and high resistance to degradation when discarded in the environment. Inexpensive rectorite has been selected to replace the commonly used bentonite as the raw clay to produce organophilic clay through a modification reaction with nonionic surfactants. Crucial properties, including swelling index, viscosity, yield point, gel strength, and suspendability, were evaluated.

Effect of casing surface roughness on the removal efficiency of non-aqueous drilling fluids

The primary function of natural gas well cementing is to provide downhole zonal isolation. However, the residual non-aqueous drilling fluid in cement and on the surface of the casing can weaken the bond of hardened cement to the casing. In this paper, the amount of remaining drilling fluid both in cement and on the casing is quantified by the fluorescent dye method, which is verified by other two methods, mass difference and laser scanning. The essential factor - surface roughness that can significantly affect the amount of residual drilling fluid - is investigated. Results show good correlations between the thickness of the remaining drilling fluid and the surface roughness. The comparison of mud removal efficiency of two commercial spacers indicates that microemulsion can remove more drilling fluid than the common spacer, as pointed out in the literature; however, microemulsion is also apt to remain on the casing and thus reduce the bonding between cement and the casing.

Technology Focus: Well Integrity and Well Control (January 2018)

Technology Focus Nonaqueous drilling fluids have been used extensively by the industry, particularly in complex drilling scenarios. They carry some concerns, however, related to environmental issues and higher initial cost, potential for lost circulation, effect of pressure and temperature on drilling-fluid density, and capacity to solubilize natural gas compared with water-based drilling fluids [water-based mud (WBM)]. The latter three concerns have implications for well integrity. It is generally accepted that the risk of induced fracture (and consequent lost circulation) is greater when using non-aqueous fluids than when using WBM. The formation-breathing phenomenon is also more pronounced with nonaqueous drilling fluids compared with WBM. Nonaqueous drilling fluids are more sensitive to pressure and temperature changes than WBM is. Thus, the density and viscosity of these fluids inside the well are more difficult to establish, increasing uncertainties about bottomhole and casing-shoe pressures. Because they are more compressible, longer periods are expected for shut-in pressure stabilization, for response delay of drillpipe pressure after choke adjustment, and for flowback to stop after the mud pumps are shut off. The gas solubility in nonaqueous drilling fluids makes the kick indicators less pronounced for its detection and increases the risk of rapid gas evolution where the pressure inside the well drops below the bubblepoint pressure. However, the solubility properties of these fluids can lead to favorable conditions also: If pressure remains above the bubblepoint as the kick is circulated out of the well, there will be no free gas and, consequently, the magnitude of pressure will be smaller. Also, no free-gas migration will occur in static conditions. All these issues have been studied extensively, especially those related to change in fluid density and gas solubility. In the list of papers recommended for additional reading, two address gas-solubility aspects in nonaqueous drilling fluids. Recommended additional reading at OnePetro: www.onepetro.org. SPE 180039 Kick-Detection Capability of Oil-Based Muds in Well-Control Situations by Harald Linga, SINTEF Petroleum Research/DrillWell, et al. SPE 185470 Thermodynamic Behavior of Olefin and Methane Mixtures Applied to Synthetic-Drilling-Fluids Well Control by D.C. Marques, Consultant, et al. SPE 180292 Mathematical Modeling of Gas in Riser by Ulf Jakob Flø Aarsnes, IRIS/DrillWell, et al. SPE 181672 Multiphase Well-Control Analysis During Managed-Pressure-Drilling Operations by Z. Ma, The University of Texas at Austin, et al.

Technology Focus: Well Integrity and Well Control

Technology Focus One of the more important aspects of well integrity during drilling operations is early kick detection. When an unintentional flow of the formation fluid into the wellbore occurs during conventional drilling operations, it must be detected promptly and the flow must be stopped, normally by closing the well. The early detection is crucial in minimizing the influx size. When the amount of formation fluid inside the well is large, especially if it is gas, the pressure inside the well will be higher during the subsequent well-control operations. This can lead to an increase in time to control the well or even to a worse situation: the loss of control. Another concern may be the amount of formation fluid to be handled at surface. Deepwater, high-pressure/high-temperature, and slimhole drilling are situations where early kick detection is mandatory. The early kick detection is accomplished with a rig equipped with the appropriate kick-detection sensors and alarms and with a rig crew trained in quickly recognizing a kick and in the shut-in procedures. However, there are situations where early kick detection becomes more problematic—for example, when operating on a floating rig because of its motions, when using non-aqueous drilling fluids because of gas solubility, or during connections. Recently, new technologies and research have been applied or developed to improve the kick-detection systems and to overcome some of the difficulties. To cite just a few examples, Development of automated kick-detection systems (one of the papers summarized here addresses kick detection during connections) Kick detection just above the bit using logging-while-drilling information Kick detection using wired drillstring Research on the effect on kick detection of gas solubility in nonaqueous drilling fluids (mineral oil, paraffin, ester, and olefins) The use of managed-pressure-drilling systems (one of the papers recommended for additional reading comments on the advantage of this technology in reducing the kick size) Recommended additional reading at OnePetro: www.onepetro.org. SPE/IADC 173153 A Barrier-Analysis Approach to Well-Control Techniques by D. Fraser, Argonne National Laboratory, et al. SPE 180047 Impact of New and Ultrahigh-Density Kill Fluids on Challenging Well-Kill Operations by T. Rinde, Acona Flow Technology, et al. SPE 180053 A Numerical Study of Gas-Kick Migration Velocities and Uncertainty by K.K. Fjelde, University of Stavanger, et al.

Benthos response following petroleum exploration in the southern Caspian Sea: Relating effects of nonaqueous drilling fluid, water depth, and dissolved oxygen

The effects of linear alpha olefin (LAO) nonaqueous drilling fluid on benthic macrofauna were assessed over a six year period at a southern Caspian Sea petroleum exploration site. A wide-ranging, pre-drilling survey identified a relatively diverse shelf-depth macrofauna numerically dominated by amphipods, cumaceans, and gastropods that transitioned to a less diverse assemblage dominated by hypoxia-tolerant annelid worms and motile ostracods with increasing depth. After drilling, a similar transition in macrofauna assemblage was observed with increasing concentration of LAO proximate to the shelf-depth well site. Post-drilling results were consistent with a hypothesis of hypoxia from microbial degradation of LAO, supported by the presence of bacterial mats and lack of oxygen penetration in surface sediment. Chemical and biological recoveries at ≥200m distance from the well site were evident 33months after drilling ceased. Our findings show the importance of monitoring recovery over time and understanding macrofauna community structure prior to drilling.

Effect on Fracture Pressure by Adding Iron-Based and Calcium-Based Nanoparticles to a Nonaqueous Drilling Fluid for Permeable Formations

This paper presents a comprehensive experimental evaluation to investigate the effects of adding iron-based and calcium-based nanoparticles (NPs) to nonaqueous drilling fluids (NAFs) as a fluid loss additive and for wellbore strengthening applications in permeable formations. API standard high-pressure-high-temperature (HPHT) filter press in conjunction with ceramic disks is used to quantify fluid loss reduction. Hydraulic fracturing experiments are carried out to measure fracturing and re-opening pressures. A significant enhancement in both filtration and strengthening was achieved by means of in situ prepared NPs. Our results demonstrate that filtration reduction is essential for successful wellbore strengthening; however, excessive reduction could affect the strengthening negatively.

Influence of Clay Content and Surfactant on the Rheology of Non Aqueous Drilling Fluids

Organophilic clays are widely used in non-aqueousdrilling fluids, mixtures of different components being used in a well bore. As bentonite claysare not naturally organophilic, they can be modified by specific treatments with surfactants (ionic or nonionic). Recent studies demonstrate the influence of clay, surfactant,and the presence of a dispersant in the rheology of fluids. In this study we verified the influence of clay, and surfactant in the production of organophilic clays using an alcoholic route for the rheology of non-aqueous fluids.As such, we performed the characterization of organophilic clays by X-ray diffraction (XRD),these non-aqueous fluids were produced according to Petrobras norms for rheological testing. The results evidenced influences of the clay / surfactant ratio on the rheology of non-aqueous drilling fluids.

Dielectric properties of nonaqueous drilling fluids from 1 MHz up to 20 GHz

Measuring the water volume and the rock textural information downhole in wells with a logging tool requires an accurate knowledge of the dielectric properties of the borehole fluid. A small error on these properties can generate significant misinterpretation of the data, especially in the presence of resistive oil-based mud (OBM) or synthetic-based mud (SBM), both of which are also called nonaqueous drilling fluid (NAF). A model predicting the complex permittivity of NAF as a function of its density and the oil/water (O/W) ratio was developed in the 1970s, but since then, the NAF compositions have changed, which modified their dielectric properties. To revisit this model, a measurements campaign was launched in July 2012 to characterize the dielectric properties of NAF. NAF that results from an emulsion of water in oil consists of many components such as emulsifiers, salt, lime, weighting material, and surfactants. Different NAF formulations were prepared and the interactions between key parameters such as the O/W ratio (90/10 to 60/40) and density (9 to 15 lbm/gal) were evaluated using a central composite design (CCD).The complex permittivities of the selected NAF compositions were measured using two set-ups covering a wide frequency range, from 1 MHz up to 20 GHz. A statistical analysis of the measurements shows that the complex permittivity of NAF depends on two main influences: brine volumetric fraction and weighting material volumetric fraction. These two parameters can respectively be expressed as a function of the O/W ratio and density. The surface quadratic model responses developed during this study are validated by measuring the complex permittivities of different NAF samples from the field.

Dielectric properties of nonaqueous drilling fluids from 1 MHz up to 20 GHz

Measuring the water volume and the rock textural information downhole in wells with a logging tool requires an accurate knowledge of the dielectric properties of the borehole fluid. A small error on these properties can generate significant misinterpretation of the data, especially in the presence of resistive oil-based mud (OBM) or synthetic-based mud (SBM), both of which are also called nonaqueous drilling fluid (NAF). A model predicting the complex permittivity of NAF as a function of its density and the oil/water (O/W) ratio was developed in the 1970s, but since then, the NAF compositions have changed, which modified their dielectric properties. To revisit this model, a measurements campaign was launched in July 2012 to characterize the dielectric properties of NAF. NAF that results from an emulsion of water in oil consists of many components such as emulsifiers, salt, lime, weighting material, and surfactants. Different NAF formulations were prepared and the interactions between key parameters such as the O/W ratio (90/10 to 60/40) and density (9 to 15 lbm/gal) were evaluated using a central composite design (CCD).The complex permittivities of the selected NAF compositions were measured using two set-ups covering a wide frequency range, from 1 MHz up to 20 GHz. A statistical analysis of the measurements shows that the complex permittivity of NAF depends on two main influences: brine volumetric fraction and weighting material volumetric fraction. These two parameters can respectively be expressed as a function of the O/W ratio and density. The surface quadratic model responses developed during this study are validated by measuring the complex permittivities of different NAF samples from the field.

Development and Field Applications of a Novel NAF in the Gulf of Thailand

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 158680, ’Pushing the Envelope of HT Drilling Fluids: Development and Field Applications of a Novel Nonaqueous Drilling Fluid in the Gulf of Thailand,’ by Kerati Charnvit, SPE, Abhijart Kongto, Fransiskus Huadi, and Sunil Sharma, SPE, M-I Swaco, and Gerard Simon, SPE, Brent Estes, SPE, and Neil Trotter, SPE, Chevron, prepared for the 2012 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 22-24 October. The paper has not been peer reviewed. A novel nonaqueous-fluid (NAF) system was designed to provide stable rheological properties with a nonprogressive gel structure and very good filtration control and filter-cake quality in wells where the expected bottomhole static temperature (BHST) exceeds 400°F. The fluid was successful in providing wellbore conditions capable of being fully logged and evaluated and, at the same time, providing effective hole cleaning with minimum effect on equivalent circulating density. The fluid has been successful in wells with temperatures from 400 to 428°F and mud weights from 11.7 to 14.5 lbm/gal. Introduction Historically, conventional NAF systems have had a good performance record in the Gulf of Thailand, providing the necessary fluid and wellbore stability to achieve successful wireline-logging operations. However, when BHST exceeds 400°F, problems have been reported during wireline-logging operation, including difficulties in moving wireline-logging tools to reach the target depth or even getting stuck, which led to nonproductive time (NPT) or loss of tools in several wells. As a result, a more robust NAF that could help minimize the NPT was requested by the operator because numerous wells being planned would have BHSTs considerably above 400°F. The first approach to solve this issue was to review and modify field engineering practices in an attempt to extend the stability of the conventional NAF formulation; however, it was concluded from this initial study that a novel NAF was required for this ultrahigh-temperature condition. On the basis of extensive laboratory testing during fluid-system development, it was determined that the combination of a new nitrogen-free emulsifier designed for thermal stability in excess of 550°F and a filtration-control package comprising a synthetic polymer coupled with a modified naturally occurring polymer provided the most stable fluid up to 525°F. Main Components Emulsifier. A new emulsifier was developed to withstand ultrahigh temperatures and provide low-viscosity, stable emulsions (i.e., low and flat gel structure). The emulsifier also contributes to high-temperature/high-pressure (HT/HP) filtration control and temperature stability of the system. This emulsifier has another benefit over the conventional amine-based emulsifiers because it does not thermally degrade and release ammonia when exposed to ultrahigh temperatures, even if the temperature limit of the product is exceeded.

Development of Organoclays for Use in Oil-Based Drilling Fluids

The organoclays are derived from bentonite clays treated in aqueous solution with surfactants, which are incorporated into the interlayer surface of clays, covering them with an organic layer; so, the naturally hydrophilic clay becomes hydrophobic. This paper proposes a study to find the dispersant media (diesel, paraffin or ester) which is more suitable for use in fluids, using the bentonite clay Cloisite Na +, treated with ionic surfactants Praepagen HY and Praepagen WB. The organoclay obtained was characterized by X-ray diffraction, and we measured the apparent viscosity and plastic dispersions. We observed the importance of the type of surfactant and dispersant amid to obtain organoclays for non-aqueous drilling fluids with the dispersants that meet existing specifications for drilling oil wells.

The consequences of using concentrated salt solutions for mitigating wellbore instability in shales

Wellbore instability in shale formation is the most troublesome and costly issue facing drilling engineers and operators. Early attempts to solve this problem recommended the application of osmosis where a chemical potential (water activity difference) is created across the wellbore in order to induce water flow out of shale. This required the addition of concentrated salts, especially when using non-aqueous drilling fluids, as a means to lower the chemical potential of the drilling fluid. While this practice may draw water out of shale, the benefit of such practice is compromised by the invasion of ions and their associated water owing to the ionic concentration difference created by the addition of salts to the drilling fluid. The invasion of ions and their associated water into the shale could change the pore fluid composition and mechanical properties of the shale, which could lead to strength reduction through cementing bonds weakening and cohesion degradation and thus matrix expansion and swelling, all of which result ultimately in shale failure.This paper analyzes prior experimental data that claims that shale generates high osmotic pressures by evaluating the experimentally measured membrane efficiency (63 data points) of shale when exposed to both aqueous and non-aqueous drilling fluids. In addition, a series of immersion tests and gravimetric measurements were performed on different shales, when exposed to concentrated aqueous solutions, to study the detrimental impact of ionic diffusion on shale stability. Moreover, biaxial stress tests were performed to investigate the impact of the invasion of water and ions on the compressive strength of shale as it interacts with concentrated aqueous solutions. Other important but ignored mechanisms that greatly impact wellbore instability in shales are also briefly addressed.Results show that while shales behaved as semi-permeable membranes, their membrane efficiencies were low (the average membrane efficiency reported was 0.034). In addition, it was shown that significant ionic invasion coupled with the flow of their associated water occurred when shales interacted with concentrated aqueous solutions. It was further observed that, shale samples failed after 48h when they were immersed in concentrated aqueous solutions having water activities that were less than that of the shale samples. Also, results show that the compressive strength of shale was altered as a result of water and ion interaction with the shale matrix and pore fluid.

Toxicity Characteristics of Drilling Mud and Its Effect on Aquatic Fish Populations

Toxicity tests are important for assessing the effects of complex chemical mixtures, such as waste drilling mud, on aquatic ecosystems. When waste drilling mud is released into the marine environment, strong ocean currents perhaps separate the drilling mud into a solid phase (SP) and a suspended particulate phase (SPP). A comprehensive assessment of drilling mud and base oil was carried out in the laboratory for acute fish toxicity (freshwater fish, marine fish, and benthic organisms) and biodegradability. The results presented in this paper indicate that the LC50 96 h for fresh water, marine and benthic organisms was in the order of base oil > SP > SSP. The 28-day biodegradability of base oil was also more than that of drilling mud. The results also showed that nonaqueous drilling fluids (NADFs) are readily biodegradable. The Spearmen results clearly showed the effects on fish populations from the discharge of drilling mud into aquatic systems. The results showed that the use of NADFs instead of water-based fluids (WBFs) would have lesser adverse impact on the envi- ronment. DOI: 10.1061/(ASCE)HZ.2153-5515.0000092. © 2012 American Society of Civil Engineers. CE Database subject headings: Drilling; Toxicity; Mud; Fish management; Aquatic habitats; Ecosystems. Author keywords: Drilling fluids; Solid phase; Suspended particulate phase; Base oil; Biodegradability.

Effect of non-aqueous drilling fluid and its synthetic base oil on soil health as indicated by its dehydrogenase activity

Drilling fluids are used for drilling natural gas, oil and water wells. These spill over into the surrounding soil at the point of drilling, which may impair soil health. A laboratory investigation was carried out to determine the effect of non aqueous drilling fluid (NADF) and synthetic base oil used with it on soil health as indicated by the dehydrogenase activity. A non-sterile sandy loam soil was treated with different amounts of NADF and base oil at a rate of 800, 8,000 and 16,000 mg kg−1. Initially, reduction in dehydrogenase activity was observed, but it increased with the incubation time. On the 60th day of incubation dehydrogenase activity in untreated control was 1.04 mg TPF g−1 h−1 whereas in the soil samples treated with NADF and the base oil (16,000 mg kg−1), the activity was 1.53 mg TPF h−1 and 1.90 mg TPF h−1, respectively, which was 72 and 82% more than in untreated control. Base oil-treated soil showed more dehydrogenase activity than that observed with NADF. Both NADF and base oil stimulated the soil dehydrogenase activity.

Metal and hydrocarbon behavior in sediments from Brazilian shallow waters drilling activities using nonaqueous drilling fluids (NAFs)

The impact of drilling oil activities in the Brazilian Bonito Field/Campos Basin (Rio de Janeiro) shell drilling (300 m) using nonaqueous fluids (NAFs) was investigated with respect to Al, Fe, Mn, Ba, Co, Pb, Cu, As, Hg, Cr, Ni, Zn, Cd, V, and aliphatic and polynuclear aromatic hydrocarbons concentrations in the sediment. Sampling took place in three different times during approximately 33 months. For the metals Al, As, Co, Cr, Cu, Cd, Fe, Ni, Mn, V, and Zn, no significant variation was observed after drilling activities in most of the stations. However, an increase was found in Ba concentration--due to the drilling activity--without return to the levels found 22 months after drilling. High Ba contents was already detected prior to well drilling, probably due to drilling activities in other wells nearby. Hydrocarbon contents also suggest previous anthropogenic activities. Aliphatic hydrocarbon contents were in the range usually reported in other drilling sites. The same behavior was observed in the case of polyaromatic hydrocarbons. Nevertheless, the n-alkane concentration increased sharply after drilling, returning almost to predrilling levels 22 months after drilling activities.

Treatment of Oil-Based Drilling Waste Using Supercritical Carbon Dioxide

Abstract Oil-based drilling fluids are essential for challenging drilling operations. However, their use requires costly handling, treatment and disposal. Supercritical fluid extraction is herein investigated as a novel technology to treat this waste. Supercritical fluid extraction employs a substance above its critical temperature and pressure as a solvent. In this state, the substance has both liquid- and gas-like properties that can be controlled by the pressure and temperature of the extraction process. In this paper, results of studies using supercritical carbon dioxide to remove the base oil from drilling waste are presented. Current work investigates the extraction of hydrocarbons (i.e. base oil) from a synthetic oil-based centrifuge underflow drilling waste. Extraction efficiencies as high as 98% have been observed. Additionally, results of both past and current studies indicate that the hydrocarbons are unchanged by the extraction process and that they may be recovered and potentially reused. Introduction In rotary drilling, drilling fluids are essential to lubricate the drill bit and circulate the drill cuttings to the surface. It is well documented that oil-based drilling muds (OBMs, sometimes referred to as non-aqueous drilling fluids or NADFs) have several advantages over their water-based counterparts(1, 2). OBMs have a higher natural lubricity, making them suitable for challenging drilling operations. Also, OBMs are less reactive with clays and shales, thereby preventing hole enlargement, resulting in smaller overall waste volumes. However, OBMs must be carefully handled and treated prior to disposal due to their potential negative environmental effects. There are a number of options available to treat and dispose of OBM drilling wastes (for example, land spreading and landfilling), however the cost of handling and disposing of drilling waste is increasing. The drilling industry is now turning to novel approaches for the treatment and disposal of drilling wastes in order to meet more stringent environmental guidelines(3). Supercritical fluid extraction (SFE) is an extraction technique that uses substances at or above their critical pressure and temperature as solvents. In the vicinity of the critical point, the liquid and vapour phases of the substance merge, producing a fluid with gas-like diffusivity and viscosity and liquid-like density(4, 5). These properties provide for favourable mass transfer of soluble waste components (i.e. hydrocarbons) from solid matrices to the bulk supercritical fluid. The density of the fluid is defined by the pressure and temperature; small changes in processing conditions can fine-tune the solvating power of the fluid(6). Additionally, supercritical fluids have zero surface tension, thereby allowing easy penetration into most matrices(4). Several studies have documented the treatment of OBM drilling waste using SFE. In 1984, a patent by Eppig et al. detailed a system suitable for the removal of organic contaminants from inorganic matrices(7). This patent specifically lists the treatment of oil contaminated drill cuttings as an application of the technology, and indicates that propane, Freon and carbon dioxide would be suitable supercritical fluids for this purpose. A later study by Eldridge investigated the use of a pilot-scale SFE system to treat oil contaminated drill cuttings from North Sea drilling platforms(8).