INTRODUCTIONAlthough a great deal has been written about the pressure and temperature behaviour of the viscosity of simple non-ABSTRACT Newtonian fluids, and an understanding of this behaviour at The theological behaviour of invert emulsion muds has been the molecular level is emerging, no consensus exists on how studied at pressures up to 1000 bar and temperatures up to to deal with concentrated suspensions. This can easily be 240°C. Theological parameters were calculated for the Bingunderstood, considering the widely different nature of nonham, Herschel-Bulkley and Cssson theological models. The Newtonian fluids, Invert emulsion muds are suspensions of Iierachel-Bulkley and Cesson modeb both give good fits to the solids and emulsions at the same time, and as there is no experimental rheograms. The Cesson model is more reliable generally accepted theological model that can be applied to for extrapolation purposes than the Herschel-Bulkley model. emulsions and suspensions, the engineering aspects of invert A pair of two similar exponential expressions were found to emulsion muds are not always based on very sound scientific be able to model the pressure and temperature behaviour of principles, Thus, while it is known that at pressures and temthe two parameters of the Casson model. The expressions, peratures encountered in the wellbore the rheology of the mud which are baaed on the relation for pure liquids derived theoretically by Eyring, contain temperature dependent pressure will be different from that measured at the surface, lack of coefficients. The simplifications inherent in the temperature the ability to quantify the effects involved has perpetuated the and pressure model are dkcussed in the light of the tempera-field practice of using theological parameters measured at atture and pressure behaviour of the viscosity of common base mospheric pressure. Traditionally the mud industry has, with oils and their constituent hydrocarbons. Field application of a few exceptions, adhered to the uee of the Bingham and power the model requires measurement of the rheology of the mud at law theological models, which have the advantage that hytwo or more temperatures and knowledge of the pressure co-draulics calculations are available for fluids obeying these modefficients relating the behaviour of the plastic viscos~ty to that els. Hence, it is not surprising that the existing techniques for of the yield point, or the Casson high shear visccgity to that prediction of downhole rheology are based on these models. of the Casson yield stress. Pressure meaauremer !S or other A number of recent publications have dealt with the problem. information are then not required. Applications can be baaed Combs and Whitmire (1) showed that the change in the viscoson Caason or Bingham theological meesurements. The rela-ity of the continuous phase is the main factor in controlling the tionships between the parameters of the Casson and Bingham change in the viscosity of the mud with pressure. Both yield models are disussed. point and plas...
Drilling waste disposal using hydraulic fracturing is often the preferred waste management option because it can achieve true zero discharge without being limited by the drilling location.This is particularly true for drilling operations in remote and challenging areas such as offshore Sakhalin Island as there is no established infrastructure for drilling waste management. This paper presents a case history of managing uncertainties and risks related to a drill cuttings re-injection (CRI) project offshore Sakhalin Island. Although there are uncertainties and risks with the CRI project in this case, regulatory requirements and the operator's commitment to zero discharge made it the preferred option for drilling waste management.Complicating the decision was a previous injection well where cuttings settling made it inoperative. Thus, the only option was to inject the oily cuttings into a deviated well intended for future use as a development well, which posed a number of risks related to the proposed CRI operation. Since this is the only option for drilling waste management and loss of this well would have delayed the drilling program and field development for at least a year, managing the risks and uncertainties related to this CRI project and assurance of a trouble-free CRI operation were critical. This paper presents monitoring and diagnostic analyses that were used for slurry design and optimization, pumping procedure design and optimization considerations, as well as solids transport modeling and planning length of shut-in intervals between batches.These quality assurance and optimization measures were proven to be effective in managing the risks and uncertainties associated with this critical cuttings injection well off Sakhalin Island.At the time of this writing, more than 100,000 bbl of slurry and fluid had been injected into this well without incident. Introduction Oil and gas exploration and production companies are responsible for managing drilling wastes in a safe and environmentally acceptable fashion that complies with regulation requirements.Tightening environmental legislation worldwide and operators' environmental policies are reducing options for drilling waste management.Subsurface re-injection of drill cuttings and used mud often is the most cost effective, environmentally acceptable method to dispose of these waste products.[1 - 13]This is particularly true for drilling operations in remote and environmentally sensitive areas such as offshore Sakhalin Island where drilling waste treatment and management facilities are usually limited in these isolated areas.
Even though shale has traditionally been considered a hydrocarbon source rock and/or seal rock, some gas bearing shales have been recognized as major reservoir rocks for unconventional hydrocarbon resources. The exploitation of gas shale across North America has generated much activity in the drilling and completion sector of the oil and gas industry, including drilling horizontal wells and multi-stage fracturing with water-based fracturing fluids. During water fracturing, the shale will interact with water and create consequences (hydration, dehydration, fractures etc.) as that happens in drilling. The consequences from this shale/water interaction will not only alter the shale mechanical properties, but also induce stress changes in the shale. These changes may induce favorable or unfavorable fractures in the shale/water interacted zones. This paper first outlines lab observations of the shale/water interactions which generating fractures in gas shale. Then, a stress model is developed with poro-elasticity effect and simulation method for studying stress changes due to shale hydration in near-fracture zones. This paper also describes a sample application of the models to investigate stress changes and potential shale failures in shale around major hydraulic fractures in shale gas. The study presented in this paper that it was mechanically possible to induce multiple secondary fractures around major hydraulic fractures via shale hydration. The modeling in this paper completes the preliminary study and provides a foundation for more complex scenarios in future studies focusing on water fracturing and horizontal well drilling in gas shale. It also provides some new ideas of optimizing hydraulic fracturing in gas shale.
Summary A new method of measuring the concentration of ions in water-based mud filtrates is described. The method, based on ion chromatography (IC), provides a tool to monitor changes in the composition of both major ions (sodium, potassium, calcium, magnesium, chloride, sulfate, and carbonate) and environmentally sensitive ions (e.g., chromium and mercury) in mud filtrate during drilling. Changes in filtrate composition are caused by mud treatment and/or mud/rock interactions; chemical logs can be used to discriminate broad lithological changes. The mud-filtrate composition is modeled with a computer-based equilibrium model. The chemical-logging method has been applied to two case studies, one of which involved operation of equipment at the rigsite. The method can be used to monitor the composition of ions not currently analyzed by the widely accepted American Petroleum Inst. (API) Standard 13B-1 procedures. Introduction Chemical composition is a critical factor in determining the performance of water-based drilling fluids and in devising procedures for their treatment. During drilling, the circulating mud undergoes continual chemical changes that arise from additions of mud products at the surface, interactions with drilled formations (the addition of drilled solids, pore-fluid influxes, and dissolution/precipitation reactions), and losses at the surface (mud discharge and retention of mud products on cuttings). In general, these changes degrade the performance of the mud and must be corrected, either by treatment or by discharge. Despite the increasing importance of water-based drilling fluids and the growing emphasis on their suitability to discharge, current rigsite monitoring of their chemical composition is limited. The widely accepted API Standard 13B-1 procedures give an incomplete analysis of the ionic composition of the drilling fluid; for example, the concentrations of sodium, sulfate, and carbonate/bicarbonate ions are not routinely monitored. Methods for determining the concentration of potassium have been the subject of some attention, although these techniques do not appear to be in routine use. Methods have also been described to monitor the concentration of certain polymers and organics and such mud solids as bentonite, but these components are not monitored routinely.
With ever-tightening environmental regulations and the green initiatives of most operators, drilling waste disposal through downhole hydraulic fracturing often becomes the preferred waste management option. This is because the technology allows drilling wastes to be handled at the drilling site to achieve true zero discharge. However, formation damage due to solid-laden slurry injection can cause large uncertainties in injection well performance and waste containment assurance. Complicating the problems are the many formation damage mechanisms that are often difficult to model with confidence. A holistic approach based on Monte Carlo simulations has been developed for modeling formation damages and their competing contributions to injection well performance and waste containment assurance. This paper presents a probabilistic approach to modeling and evaluating associated uncertainties, particularly geology and formation damage, and their impacts on waste containment assurance and risk assessment in cuttings re-injection operations. Probabilistic results are important in designing cuttings injection operational procedures, and risk management, and in obtaining regulatory approval. Examples are given to illustrate how to model formation damage caused by intermittent slurry injections and its impacts on waste containment. Monitoring and validation procedures are given to increase quality assurance through operational data evaluation and risk-based modeling result validation. Introduction Oil and gas drilling and production produce wastes. For example, the principal waste product of the drilling process is often oil-contaminated drill cuttings. One of the preferred waste management options is downhole injections into a deep geological formation through hydraulic fracturing. This technology is often known as Cuttings Re-Injection (CRI) although other designations have been used, even if the injected material likewise includes production wastes such as produced sands, tank bottoms, produced waters and other by-products from oil/gas production.[1–11] Figure 1 is a schematic of a cuttings re-injection process. Very briefly, a drill cuttings injection operation involves the collection and transportation of solid waste from solids control equipment (in this case a shale shaker) on the rig to a slurrification unit, where the cuttings are ground (if needed) to small particles in the presence of water to make a slurry. The slurry is then transferred to a slurry holding tank for final slurry rheology conditioning. The conditioned slurry is pumped through a casing annulus or a tubular into subsurface fractures created by injecting the slurry under high pressure into the disposal formation. The waste slurry is often injected intermittently in batches into the disposal horizon. Each batch injection may last from a few hours to several days or even longer, depending upon the batch volume and the injection rate.
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