Gao, Jia Jia (Department of Civil & Environmental Engineering, National University of Singapore) | Lau, Hon Chung (Department of Civil & Environmental Engineering, National University of Singapore) | Sun, Jin (Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences)
Conventional drilling design tends to inaccurately predict the mud density needed for borehole stability because it assumes that the porous medium is fully saturated with a single fluid while in actuality it may have two or more fluids.
This paper provides a new semi-analytical poroelastic solution for the case of an inclined borehole subjected to non-hydrostatic stresses in a porous medium saturated with two immiscible fluids, namely, water and gas. The new solution is obtained under plane strain condition. The wellbore loading is decomposed into axisymmetric and deviatoric cases. The time-dependent field variables are obtained by performing the inversion of the Laplace transforms. Based on the expansion of Laplace transform solution, we derive the unsaturated poroelastic asymptotic solutions for early times and for a small radial distance from an inclined wellbore. The model is verified by analytical solutions for the limiting case of a formation saturated with a single fluid. The impact of unsaturated poroelastic effect on pore pressure, stresses and borehole stability is investigated.
Our results show that the excess pore pressure due to the poroelastic effect is generally higher for the saturated case than the unsaturated case due to the large difference between the compressibility of fluid phases. The time-dependency of the poroelastic effect causes the safe mud pressure window of both the unsaturated and saturated cases to narrow with increasing time with the unsaturated case giving a narrower safe mud pressure window. Furthermore, this window narrows with increasing initial gas saturation. The commonly used assumption that the formation is fully saturated by one fluid tends to be conservative in predicting the mud density required for borehole stability.
This new semi-analytical poroelastic solution enables the drilling engineer to more accurately estimate the time-dependent stresses and the pore pressure around a borehole, thus allowing him to design the mud weight to ensure borehole stability.
In this paper, we present for the first time, a classification system for naturally-occurring gas hydrate deposits existing in the permafrost and marine environment. This classification is relatively simple but highlights the salient features of a gas hydrate deposit which are important for their exploration and production such as location, porosity system, gas origin and migration path. We then show how this classification can be used to describe eight well-studied gas hydrate deposits in permafrost and marine environment. Potential implications of this classification are also discussed.
This paper describes the interaction between hydraulic fractures and the multi-porosity system of matrix porosity and natural fracture porosity in shale reservoirs. During the process of hydraulic fracturing, a complex fracture network consisting of primary and secondary hydraulic fractures as well as natural fractures is created. It is postulated that only shale porosities connected with this network will contribute to hydrocarbon production. Furthermore, we propose a way to maximise well productivity by injecting microsized proppants that are less than 150 μm (100 mesh) into the natural fractures and secondary hydraulic fractures to prevent them from closing and thereby increasing the stimulated reservoir volume. The size of the micro-sized proppant should be designed to be between one-seventh and one-third the aperture size of the natural fractures. In addition, various materials for micro-sized proppants are proposed and discussed. Of these, hollow glass microsphere shows more promise because of its light density and track record of being used as an additive material in the oilfield. Although limited laboratory experiments and field tests have shown encouraging results of using micro-sized proppants to enhance the productivity of Barnett shale, more research is warranted to optimize the use of these micro-sized proppants in production enhancement in various shale formations.
Introduction Of the three permafrost regions, our calculations show Mohe Basin has the thickest hydrate stability (1300 m). This is followed by Qinghai-Tibet Plateau (1200 m) and Qilian Mountain (800 m).
This paper identifies several best practices for improving employee competency and productivity. They include aligning reward and promotion practices with company core values, promoting those who are already leading and have the capacity to perform at the next level, and using both internal and external benchmarking to help employees to set stretch goals for competency training and improving productivity.
Shale reservoirs contain predominantly micro and mesopores (<50 nm), within which gas is stored as free or adsorbed gas. Due to the ultra-small pore size, multiple transport mechanisms coexist in shale reservoirs, including gas slippage, Knudsen diffusion of free gas and surface diffusion of adsorbed gas. In this work, we propose a new transport model, valid for all ranges of Knudsen number, which combines all transport mechanisms with different weighting coefficients. To quantify the effects of influence factors, we introduce the compressibility factor for real gas effect and effective pore radius for gas adsorption and stress dependence. The model is proven to be more accurate than existing models since the deviation of the analytical solution of our model (3%) from published molecular simulation data is lower than that of existing models (10~20%). Based on this model, we compare (1) the contribution of each transport mechanism to gas transport in pores of different radii, (2) shale permeability measured in laboratory and at reservoir conditions, and (3) permeability of nanopores and natural fractures. It is found that gas transport is dominated by gas slippage and surface diffusion when the pore radius is over 10 nm and below 5 nm, respectively. Knudsen diffusion only becomes significant when the pore radius is between 2 and 25 nm and pore pressure is below 1000 psi. Furthermore, laboratory measurements usually over-estimate shale permeability. We also propose a promising enhanced gas recovery method, which is to open and prop up closed natural fractures using micro size proppants.
In today's high-stakes E&P operating environment, achieving operational excellence is key not only to profitability but also obtaining a license to operate. Doing so requires E&P companies to have competent staff who are qualified to perform their jobs professionally at all levels of seniority. As technology and the regulatory environment change, continuous education for technical professionals is not only desirable but necessary. Competency-based training (CBT) is one of the most effective ways to ensure competency development in E&P professionals. Unlike traditional training, CBT focuses on helping the learner to master well-defined job-related competencies. The hallmarks of CBT are repeatability and reproducibility of results. Repeatability is the ability of the same learner to achieve consistent results whereas reproducibility is the ability of multiple learners to achieve the same consistent results. This paper discusses the ten elements of CBT in order to achieve repeatability and reproducibility.
Li, Shidong (Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research A*STAR) | Hadia, Nanji J (Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research A*STAR) | Lau, Hon Chung (National University of Singapore) | Torsæter, Ole (PoreLab Research Center, Department of Geoscience and Petroleum, Norwegian University of Science and Technology) | Stubbs, Ludger P (Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research A*STAR) | Ng, Qi Hua (Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research A*STAR)
Oil and gas industry is witnessing a rapid increase of interest in application of nanotechnology. Since last few years, nanotechnology is being studied as an alternative enhanced oil recovery (EOR) method and laboratory experiments have shown its potential. However, the adsorption behavior of nanoparticles in porous media and underlying mechanisms for improving oil recovery are still not well understood. The objective of this study was to investigate silica nanoparticles adsorption and displacement mechanisms at the pore scale within a micromodel. Another objective was to stabilize silica nanoparticles in the presence of crude oil at a high salinity and a high temperature for a longer period of time.
A turbidity scanner was utilized to test stability of silica nanoparticles suspension in the presence of crude oil under 60°C. Turbidity stability index was used to evaluate stability of nanoparticles suspension and hydrochloric acid (HCl) was used as stabilizer to improved stability of nanoparticles suspension. The interfacial tensions (IFT) and contact angle between crude oil and the nanoparticles suspension with stabilizer were also measured. Both single-phase and two-phase flooding experiments were conducted for nanoparticles with and without stabilizer by using glass micromodels to visualize the nanoparticles adsorption and displacement behavior at the pore scale. Oil recovery was determined with image analysis to evaluate the potential of these nanoparticles for EOR applications. In addition, microscope images were taken and analyzed to investigate EOR mechanisms of nanoparticles suspension.
Results of turbidity scanner showed nanoparticles behavior changed from aggregation to sedimentation. Silica nanoparticles suspension with HCl showed much better stability than the one without HCl under 3.8 wt. % synthetic sea water and 60°C condition. Wettability alteration between crude oil and water were observed with silica nanoparticles. For single-phase visualization flooding experiments, nanoparticles suspension with a stabilizer had less adsorption than the one without a stabilizer, and it could flow through micromodel without significant plugging. Nanoparticles adsorption can alter wettability of the micromodel to more water-wet. For two-phase visualization flooding experiments, injection of silica nanoparticles suspension with a stabilizer had better EOR result under high flow rate and can increase oil recovery about 3%. Wettability alteration and emulsification were proposed as main EOR mechanisms for nanoparticles.
Silica nanoparticles stability behavior in the presence of crude oil under a high salinity and a high temperature was studied and the stability of nanoparticles suspension was quantified by using turbiscan stability index. Adding HCl as a stabilizer can reduce adsorption of nanoparticles in micromodel and avoid plugging. Enhanced oil recovery mechanisms of nanoparticles were investigated by using visualization micromodel flooding for better understanding of nanoparticles flooding.
Gas hydrate has been found both in the permafrost and deep ocean in China. However, due to easier access, much lower well cost and proximity to existing gas pipelines, gas hydrate in the permafrost is more attractive for commercial development. In this paper we examine the published data on gas hydrate exploration in various Chinese permafrosts, identify the key technical challenges and suggest directions for future study.
Our study has identified Qilian Mountain Permafrost, Mohe Basin and Qinghai-Tibetan Plateau as the three permafrosts with highest potential for gas hydrate development. Of the three, only Qilian has confirmed occurrence of gas hydrate by coring. From the perspective of field operations, Qilian ranks highest in potential for development due to its proven hydrate occurrence, thickness of hydrate bearing layer and proximity to existing gas pipelines. Mohe ranks second due to its benign operating conditions. However, it lacks existing gas pipelines. Qinghai-Tibetan Plateau ranks third due to its high elevation which limits access and lack of oilfield infrastructure.
We found that the key subsurface uncertainty is the gas hydrate saturation. There is little information on it for all three permafrosts. Other subsurface uncertainties include the thickness of the permafrost, geothermal gradient beneath the permafrost, porosity, gas hydrate composition and permeability of the hydrate-bearing layer. Future research needs to determine these reservoir properties accurately.
Examination of core samples and logs from Qilian shows that gas hydrate distribution is discontinuous both vertically and areally. Therefore, a better way to quantify the uneven hydrate distribution in the reservoir is needed for reservoir engineering calculations.
Current estimates of well production rate by reservoir simulation are sub-commerical and probably due to the assumption of pure methane hydrate which limits the thickness of the gas hydrate stability zone. Also, the assumption of using horizontal wells for hydrate production may be optimistic due to shallow depths and the discontinuous nature of hydrate distribution. Consequently, new recovery methods besides depressurization and thermal stimulation will be needed to increase the well production rate.
Furthermore, we have identified a number of similarities in production engineering aspects of gas production from hydrate and coalbed methane (CBM) wells. Common challenges include reservoir depressurization by water production, solids production, need for artificial lift and difficulty in drilling long horizontal wells in shallow reservoirs. Therefore, some best practices from CBM production, such as pad drilling, artificial lift and water treatment methods, may be usable for gas hydrate production.
As petroleum projects becomes more international, there is more need for the petroleum professional to communicate across cultural boundaries. Intercultural competency on the part of the petroleum professional begins with an awareness of three types of cultures at work in the workplace: national, corporate and personal. Based on proven research in the field of cross-cultural communication, we propose using the Cultural Onion Model (