查看更多>>摘要：The deep exploitation of silty reservoirs which store large scales of natural gas hydrate using the replacement method is of great significance for meeting the clean energy demand and reducing carbon emissions. Investigating the effects of CH4-CO2 replacement on the strength and deformation properties of hydrate-bearing silty sediments (HBSSs) plays a vital role in assessing the possible risks and conducting corresponding designs of the silty reservoirs during natural gas production. For that reason, this paper designs a series of CH4-CO2 replacement experiments on the HBSSs followed by the shear tests, and the deformation and strength behaviors of this material during the replacement were obtained and analyzed. The results show that HBSSs presents final compression behaviors after CH4-CO2 replacement while the dilation behaviors could appear due to CH4 hydrate dissociation at the initial stage of replacement. The replacement reduces the Elastic modulus but causes less change on the peak strength and deformation behaviors of CH4 HBSSs. This material also shows the relatively similar stress-dilatancy behaviors before and after partial replacement. The key influence of CH4-CO2 replacement on silty reservoirs may be located in the deformation of HBSSs during the replacement and the Elastic modulus reduction after replacement. These results in this study are wished to provide potential theoretical support for predicting the geo-mechanical response of silty reservoirs if hydrate production is applied using the CH4-CO2 replacement method.
查看更多>>摘要：Efficient hole cleaning in drilling operations is essential to ensure optimum penetration rates. This complex problem involves the simultaneous analysis of multiple parameters, including cuttings characteristics, fluid rheology, and annulus space geometry. The effect of the mud density increase due to the cuttings concentration, which itself is a function of the settling velocity and rate of penetration (ROP), must be considered for accurate calculations of the equivalent circulation density (ECD). Mechanical Specific Energy (MSE) models have been widely used in bit selection, drilling efficiency quanti-fication, drilling performance monitoring, drilling performance optimization, and ROP improvement. We attempted to employ MSE for optimized hole cleaning and controlled ECD. Cuttings concentration was integrated with the drilling MSE, which was calculated to determine the effect of different drilling parameters on hole cleaning and ECD. We proposed a new model for predicting the ECD in vertical and deviated wellbores that takes fluid and formation properties, as well as wellbore and drill string geometry and drilling operational parameters, into account. The model predicts the cuttings concentration and equivalent circulation density in vertical and deviated wells. The workflow implements the critical and settling velocity models, which aids in optimizing drilling performance and hole cleaning. The developed model was used to study the effect of different drilling parameters on ECD and help engineers optimize their operational parameters. Integrating the drilling operational parameters to provide controlling options to drillers as they monitor ECD values while maintaining safety and optimizing the drilling job is critically important.
Rayhani, MahsheedSimjoo, MohammadChahardowli, Mohammad
18页
查看更多>>摘要：Recent studies have shown that although low salinity waterflooding leads to promising EOR impacts, it is to blame for the formation of unwanted water-in-oil emulsions. Thus, this study aims to explore the effect of water chemistry, namely ionic strength and ion types on the stability of natural water-in-oil (W/O) emulsions at the reservoir temperature of 80 degrees C. To this end, seawater and its dilutions with different concentrations of potential determining ions (PDIs) were used as the aqueous phase. The experimental study was performed by tracking the emulsion droplet size distribution, phase separation study and also IFT measurements. Results showed that the higher the ionic strength of the aqueous phase, the lower the W/O emulsion stability, which could be explained based on the salting-out mechanism. It was found that the IFT parameter did not significantly contribute to the emulsion stability. Regarding the effect of ion types on the stability of emulsions prepared by eight-time diluted seawater with different PDIs, the trend was Mg2+ >= Ca2+ > SO42-. These observations were described in the light of the higher tendency of divalent cations to bond with crude oil polar components. As to the phase separation study, the amount of expelled water in the presence of Mg2+ was 15 vol% of the initial water, compared to 24 vol % for Ca2+ and almost half for SO42- after one-day aging. It was also found that the co-existence of sulfate with divalent cations improved the emulsion stability, while the less stable emulsions were obtained by the sulfaterich brine. This was further supported by the droplet size distribution profile in which a more uniform profile was obtained for emulsions with the co-existence of sulfate and divalent cations as compared to the sulfate-rich samples. Results of this study addressed that the ionic strength of the aqueous phase coupled with its ionic content regulates the emulsion stability, such that there exists a specific range of salinity and ion concentration beyond that the emulsion stability may impair.
查看更多>>摘要：One of the challenging issues during underbalanced drilling (UBD) is the prediction of frictional loss in the presence of three-phases of drilling fluid, cuttings, and air. In the current work, three innovative machine learning-based algorithms based-on Gradient tree boosting (GTB), Adaptive neuro-fuzzy inference system (ANFIS), and Extreme learning machine (ELM) have been suggested to calculate the frictional loss in gas-based drilling fluids containing cuttings in inclined annuli. A number of 216 real frictional pressure loss data in terms of hole inclination, pipe rotation, rate of penetration, and flow rates of each phase have been collected to train and validate the frictional pressure loss models. The visual and statistical comparisons of the frictional pressure loss models and actual values reveal that models have a fascinating ability in prediction of the frictional pressure loss for inclined wells. Besides, the GTB model has the best performance with R-2 = 1, RMSE = 0.0031, MRE = 0.415, STD = 0.0023, and MSE approximate to 0 in comparison with actual frictional pressure loss values. Furthermore, an exciting sensitivity analysis has been used to identify the effectiveness of each operational parameter on frictional pressure loss for inclined annuli. Due to these facts, the current work can be applied as an assistant in the development of drilling simulators in complicated field conditions.
Mirabbasi, Seyed MortezaAmeri, Mohammad JavadAlsaba, MortadhaKarami, Mohsen...
16页
查看更多>>摘要：One of the most challenging issues during drilling operations is lost circulation, which can cause several problems that could lead to increasing the non-productive time (NPT) and drilling cost. Wellbore strengthening techniques have been applied as a well-known approach to increase the mud weight window by improving mud cake properties or adding lost circulation materials (LCMs) to the drilling fluid. The success-to-failure ratio of remedial or preventive solutions during the field operation is highly dependent on the appropriate selection of wellbore strengthening strategy. Initial studies, which have often focused on trial and error and operational practices, have not provided a clear understanding of fundamental mechanisms and performance of LCMs in strengthening of a formation. Hence, in the last decades, several analytical and numerical studies, as well as experimental evaluations have been performed by numerous researchers to simulate the fluid loss process and LCM effectiveness. Conducting a comprehensive and well-designed experimental investigation can be a more applicable and cost-effective approach to select proper wellbore strengthening method and recommend the best drilling fluid formulation to treat the loss zone. The aim of this paper is to present an overall review on the various published experimental investigations, to assess the different aspects of lost circulation and wellbore strengthening theory. This extensive literature review collects limitations, advances, and differing opinions from experts. It also broadens the scope for future work and helps in solving industrial problems from an operational point of view.
查看更多>>摘要：Foams have high apparent viscosity when flowing in porous media, therefore foam flooding could significantly improve unfavorable mobility ratios, increase sweep efficiency, and enhance oil recovery. However, the applications of foam flooding in high-temperature and high-salt reservoirs are seriously restricted as foam systems often have inferior foamability and stability in these reservoirs. In this study, to improve foam flooding effectiveness in high-temperature and high-salt reservoirs, novel foam systems with excellent stability and plugging capacity are developed by combining surfactants, additives, and polymers. The performance of bulk foam, physical properties of the solutions, and properties of foam systems in core-flow experiments are investigated to determine the synergistic effects among the components of the foam systems and their foamability and plugging effect in cores. In foam systems with sodium alcohol ether sulfate (AES) and dodecylhydroxypropyl sulfobetaine (DHSB) as surfactants, and dodecanol as additive, the combination of the components makes surface tension decreased and surface dilatational modulus increased, therefore the foamability and stability of the systems are improved. The results of core-flow experiments under high-temperature and high-salt conditions show that these combined systems require low injection rate for foam generation in reservoirs, which is beneficial for foam regeneration in reservoirs. Moreover, to further improve the foam performance, a hydrophobically associating water-soluble polymer (HAWP) is employed. The interactions between HAWP and the surfactants reduce the critical association concentration of HAWP, and result in the increase of solution apparent viscosity and foam stability. The results of core-flow experiments under high-temperature and high-salt conditions show that polymer-enhanced foam systems could significantly increase the sealing pressure, widen the sealing permeability range, and deal with the gas-channeling problem of foam flooding. These foam systems could provide a potential technical pathway for improving the effectiveness of foam flooding in high-temperature and high-salt reservoirs.
查看更多>>摘要：Abundant oil potential has been confirmed in the Eocene Shahejie Formation (Es) in the Chezhen Sag, but the genetic mechanism of its reservoir has not been fully understood. Based on core observation, thin-section identification, scanning electron microscopy (SEM), X-ray diffraction, and formation pressure measurement, the factors controlling the quality of glutenite reservoirs in the Shahejie Formation in the Chezhen Sag were revealed. The petrophysical structure, depositional facies, diagenesis, and formation overpressure jointly control the development and evolution of glutenite reservoirs. Reservoirs with high composition maturity exhibit better physical properties. Depositional facies control the development of high- and poor-quality reservoirs but have little influence on the physical properties of medium-quality reservoirs. Compaction is the main factor for reducing reservoir porosity during burial, and the cementation of carbonate and clay minerals affects the reservoir quality to some extent. Each secondary structural zone shows different dissolution models. The reservoirs in the steep slope zone are in a closed system with weak dissolution, hardly contributing to improving the reservoir porosity. The dissolution of reservoirs in the depression zone has been enhanced; however, the migration of dissolution products is restricted because of the closed reservoirs, causing the redistribution of pore space and limited contribution to improving the physical properties. The reservoir in the gentle slope zone is in an open system with a shallow buried depth, and severe dissolution can effectively improve the reservoir's physical properties. A grading assessment scheme is proposed based on the depositional facies, diagenesis, and formation overpressure, and favorable exploration zones are predicted. The western part of the gentle slope zone in the upper part of the Es4 member and the eastern part of the steep slope zone in the lower part of the Es3 member of the Chezhen Sag are the principal target areas for exploration.
Rasool, Muhammad HammadZamir, AsifElraies, Khaled A.Ahmad, Maqsood...
10页
查看更多>>摘要：Ionic liquids are well-liked drilling fluid additives for inhibiting hydrates and modifying mud rheology. However, preparation of ionic liquid is costly and imidazolium based ionic liquids have been found to be severely toxic. Deep Eutectic Solvent (DES) is a non-toxic and cheaper alternative of traditional ionic liquids. In this research, inhouse prepared, Choline chloride and Urea based DES has been used as a drilling fluid additive in water based mud. Micro-DSC has been used to study the induction time of methane gas hydrates at 114 bar between -20 degrees C to 20 degrees C. Drilling fluid rheology and properties have been determined by following AP1 13B-1 standards. The results of Micro DSC evidenced that the addition of DES delayed the induction time of the hydrates up to 24.3%, improved the YP/PV of the drilling fluid and also resulted into 20% and 14.5% reduction in filtrate volume and mud cake thickness respectively. Moreover, based upon the outcomes of characterizations i.e. Zeta potential, XRD and FTIR, it is proposed that the improvement in mud rheology is due to the change in clay's size and structure on interaction with DES. Consequently, the DES inhibits the hydrate formation and alters the mud rheology by its excellent ability to form hydrogen bonds with hydrates' crystals and clay granules respectively.
查看更多>>摘要：Multi-lateral well construction is in high demand in both petroleum industrial and commercial sectors. Compared with the traditional gel-breaking fluids used in multi-lateral well completion, autonomously self-gel-breaking completion fluids in a certain downhole environment have specific challenges in development and performance. In this work, focus was on self-gel-breaking capacity demonstrating controllably heat-triggered self degradation of rheological modifier involved in the newly constructed completion fluid. The self-degradation strategy was first analyzed for the fundamental polymeric additives, and then xanthan gum with a high pyruvate content, as the most crucial rheological additive, was provided of special conformational transition from helix to lattice structure due to sidechain mutual repulsion effect, in combination to tests of advanced technologies such as molecular weight, infrared spectroscopy, dynamic viscosity, elastic modulus, and micromorphology. This facile strategy can be applicable for the control of xanthan thermal degradability that directly responses to self-gel-breaking capability of completion fluid. Finally, several key performance such as reservoir protection and self-gel-breaking capability for the newly developed completion fluid were evaluated to validate its promising gel-free application in the construction of multi-lateral wells.
查看更多>>摘要：The development characteristics of organic matter pores (OMPs) in shales is fundamental to the gas-bearing property of the shales. Detachment is one of the most common types of structural deformation in shale formations. To investigate the characteristics of OMPs in shear-deformed shale and the associated effects on the pore structure of shale gas reservoir, two sets of detachment zones and the intercalated non-detachment zone of shale formations in the Niutitang Formation of the Well XAD1 are studied. Based on scanning electron microscope observations and low-pressure gas adsorption tests, the impacts of shear on the shale pore structure are evaluated quantitively and the deformation mechanism for OMPs in shale is established. Results indicate that the dominant pore type of shale in the Niutitang Formation of the Well XAD1 is OMPs. With the mineral rheology, organic matters are enriched in the clay gouge, which are more prone to shear deformation compared with those outside the gouge. Under shear, pores developed within the organic matter experienced directional elongation and compression, decreasing the pore sizes and lowering the volumes of the corresponding pores 30 nm; and the contact surface between organic matter and minerals becomes dislocated and open, increasing the volumes of the corresponding pores 30 nm. The effect of shear on OMPs is dominated by pore reduction. The volume loss ratio of shale micropores in detachment zones is the highest which can reach over 90%. The impact of shear on pore structures of non-detachment zone cannot be neglected within the thickness range of 5-20 m from the detachment surface, and the degree of pore reduction gradually decreases as the distance from the detachment zones increases. It is indicated that the detachment and its adjacent horizons are not favorable for shale gas exploration because of the low porosity and adsorption capacity.
NSTL
Elsevier