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Vipulanandan, Cumaraswany (University of Houston -CIGMAT) | Raheem, Aram (CIGMAT- University of Houston) | Basirat, Barhar (University of Houston - CIGMAT) | Mohammed, Ahmed (CIGMAT-University of Houston) | Richardson, Donald Alexander (RPSEA)
Drilling muds are used in oil, gas, and geothermal well drilling, and fluid loss and filter cake formation are critical issues related to successful operations. Also, the filter cake formation and fluid loss are affected by high pressure and high temperature (HPHT) in the borehole. Rate and total fluid loss from drilling mud can affect the performance of the drilling mud and well safety. Hence, it is critical to quantify not only the rate of fluid loss process but also the changes in the filter cake formation during the fluid loss process. Past studies have assumed that the permeability and solid fraction in the filter cake remained unchanged during the formation of the cake and the fluid loss was directly propositional to the square-root of time (API Model).
In the experimental part of this study, fluid loss tests were performed for 420 minutes on 2 percent and 8 percent bentonite drilling muds at 100 psig pressure and 100oC temperature. A new kinetic hyperbolic model was developed based on satisfying the basic governing conditions during fluid loss and assuming that the permeability and solid content during the filter cake formation changes with time, temperature and pressure. The new kinetic model was verified with results from various HPHT fluid loss studies reported in the literature and HPHT experiments performed during this study. The new kinetic model prediction was also compared to the API model, and it predicted both short-term (up to 30 minutes) and long-term fluid losses very well. Hence, the new kinetic model can be used to better model the filter cake formation and filter loss in real time as functions of changes in permeability and solid content in the filter cake.
Summary In this paper, we investigate the change in oil effective permeability () caused by fracturing‐fluid (FF) leakoff after hydraulic fracturing (HF) of tight carbonate reservoirs. We perform a series of flooding tests on core plugs with a range of porosity and permeability collected from the Midale tight carbonate formation onshore Canada to simulate FF‐leakoff/flowback processes. First, we clean and saturate the plugs with reservoir brine and oil, and age the plugs in the oil for 14 days under reservoir conditions (P = 172 bar and T = 60°C). Then, we measure before (baseline) and after the leakoff process to evaluate the effects of FF properties, shut‐in duration, and plug properties on regained permeability values. We found that adding appropriate surfactants in FF not only significantly reduces impairment caused by leakoff, but also improves compared with the original baseline for a low‐permeability carbonate plug. For a plug with relatively high permeability (kair > 0.13 md), freshwater leakoff reduced by 55% (from 1.57 to 0.7 md) while FF (with surfactants) reduced by only 10%. The observed improvement in regained is primarily because of the reduction of interfacial tension (IFT) by the surfactants (from 26.07 to 5.79 mN/m). The contact‐angle (CA) measurements before and after the flowback process do not show any significant wettability alteration. The results show that for plugs with kair > 0.13 md, FF leakoff reduces by 5 to 10%, and this range only increases slightly by increasing the shut‐in time from 3 to 14 days. However, for the plug with kair < 0.09 md, the regained permeability is even higher than the original before the leakoff process. We observed 28.52 and 64.61% increase in after 3‐ and 14‐day shut‐in periods, respectively. This observation is explained by an effective reduction of IFT between the oil and brine in the pore network of the tight plug, which significantly reduces irreducible water saturation (Swirr) and consequently increases . Under such conditions, extending the shut‐in time enhances the mixing between invaded FF and oil/brine initially in the plug, leading to more effective reductions in IFT and consequently Swirr. Finally, the results show that the regained permeability strongly depends on the permeability, pore structure, and Swirr of the plugs.
Wang, Youhua (China Petroleum Offshore Engineering LTD) | Shu, Fuchang (Hubei Hanc New-tech Institute) | Xiang, Xingjin (Hubei Hanc New-tech Institute) | Zhang, Yan (Hubei Hanc New-tech Institute) | Luo, Gang (Hubei Hanc New-tech Institute) | Huang, Mingzhao (China Petroleum Offshore Engineering LTD.)
Abstract Waste water-based drilling fluids have some characteristics, such as complex chemical composition, colloidal stability, high COD (Chemical Oxygen Demand), low BOD (Biochemical Oxygen Demand)/COD ratio and poor chemical and biological degradation. As a result, such treatments as biochemical, chemical oxidation or membrane separation process has the deficiency of poor adaptability, poor treatment efficiency and high running costs. This paper has studied the treatment technology of low pressure distillation process for waste water-based drilling fluids. This technology has been applied in four wells of CPOE5 platforms in Dagang oilfield. The field application results have shown that this technology used to treat waste water-based drilling fluid can efficiently reduce COD, especially has good adaptability to different kinds of drilling fluids. The treatment technology studied in this paper can treat wastewater's COD to lower than 150mg/L. The disposed waste-water can reach the class II water quality requirements of China national standards (integrated wastewater discharge standard, GB8978-1996) and can be directly discharged into sea. This technology can control the influence and harm of waste drilling fluid on marine environment and meet the requirements of offshore environmental protection.
Abstract In many cases, the primary waste management challenge facing operators is drilled cuttings generated using oil- or synthetic-based fluids (OBF, SBF). Low temperature thermal desorption units (TDUs) are commonly used treatment systems for removing oil from cuttings. The oil recovered from the thermal desorption process is often reused to make oil-based fluids. However, base oils change during the thermal desorption process, and these changes can have a detrimental impact on the performance of the base oil. In some cases the base oil can break down. Typically the base oil used to formulate an OBF or SBF is selected for economical, drilling and logistical reasons and rarely, if ever, the thermal properties of the base oil. The thermal treatment company is left to determine how best to recover the oil so that the thermal degradation is minimal and the oil is suitable for reuse. To lower energy consumption and preserve the performance of the base oil, it is important to identify a base oil that has either a lower temperature for desorption or higher resistance to thermal degradation during the thermal desorption process. Ideally, a base oil would be chosen that incorporated both properties. The results of this study show that by correctly evaluating and selecting the base oil, the operator can benefit from using a fluid that may be much more suitable for reuse and will require much less energy to thermally treat. This paper describes how to achieve both of these goals using Thermal Gravimetric Analysis, Gas Chromatography / Mass Spec and a low-temperature retort. Determining the optimal desorption temperature is also an important factor. The oils recovered using these methods contain no oxygenated products and exhibit little thermal degradation. Residual oil from on cuttings is less than 1% (w/w). A practical methodology for base oil selection also is included in this discussion. Introduction Thermal desorption technology is designed to produce oil-free (or ultra-low TPH) solids for disposal by distilling off oils from the cuttings and recovering oil to be re-used for drilling fluid. However, base oils can change during the thermal desorption process, and these changes can have a detrimental impact on the performance of the base oil. Highly refined, ultra low aromatic, highly saturated, mineral- or synthetic- based oils may "crack" when exposed to the level of thermal energy required to render cuttings suitable for disposal. The process may also create aromatics and other undesirable unsaturated hydrocarbons that can affect the toxicity of the drilling fluid. The use of a base oil with higher resistance to thermal degradation during the thermal desorption process can allow the operator to recover and continue to reuse recovered base oils with minimal impacts on fluid and environmental performance. Modern TDUs have variable temperature control. If the oil on cuttings can be removed at a lower temperature, significant savings can be realized by the operator because less energy will be required by the TDU to reach the required less than 1% residual oil on cuttings. Therefore, it is important to identify a base oil that has a lower temperature for desorption so that it may be effectively removed from cuttings at a lower temperature. A further benefit of the lower temperature will be less inherent thermal degradation of the base oil. The ideal base oil choice would be one with both high resistance to thermal degradation as well as low desorption temperature. This study was conducted to help establish a reliable methodology for selecting the best base oils for use in drilling fluid systems where the thermal desorption process will be used to process cuttings and recover base oil for re-use. Base Oil Screening, Selection and Testing Nineteen base oils were screened using Thermal Gravimetric Analysis (TGA). The screening identified those base oils with a narrow evaporation range and relatively lower boiling points. Base oils were examined in air and under nitrogen; no significant differences were seen between the TGA results for oils in air and those under nitrogen (Table 1).
Abstract The main objective of using selective flocculation is to increase the efficiency of the fluid system and the solids-control equipment. Removing drill cuttings from the fluid system is important for increasing the drilling efficiency and success of the overall operation. Selective flocculation is proven to efficiently remove drilled solids, especially smaller- or colloidal-sized particles. The performance of drilling fluid components increases because larger quantities are allowed to interact with the drilled formation, which is preferred. This process provides various benefits, including decreased water consumption, which reduces requirements for additional new fluids to be mixed for dilution and consumption of sustaining properties for rheology, filtration control, and inhibition. The design process focuses on the operation of centrifuges but begins by performing a detailed evaluation using specialized equipment of all solids-control equipment available on the drilling rig, from the shakers to centrifuges. Damaged parts and accessories are repaired and/or replaced, and a simple barite retrieval system and an array of valves for the injection of a concentrated flocculant solution composed of a specialized clay polymer are installed in the centrifuges. The flow necessary for operation of the centrifuges is separated from the drilling circuit as the design current. The specialized polymer solution is injected, and the process ends with the arrangement of injection rates to obtain an output current with a clay content value measured using a methylene blue test (MBT) at zero or near zero. This current's properties must remain close to those of a new fluid without weighting material. When the treatment was evaluated, an increase in solids-control equipment efficiency of approximately 10% was obtained, and a 12% reduction in total new drilling fluid volume was observed, which could be optimized up to approximately 30%. Savings in water consumption were directly proportional, and cost savings were influenced by the reduced consumption of fluid products.