Low-pressure Reservoir Research Articles

A workflow to estimate shale gas permeability variations during the production process

Gas flow behavior in the tight shale porous matrix is complex due to the involvement of multiple physical processes. Pore size reduces as the effective stress increases during the production process, which will reduce the intrinsic permeability of the porous media. Slip flow and pore diffusion enhance gas apparent permeability, especially under low reservoir pressure. Adsorption not only increases original gas in place (OGIP) but also influences gas flow behavior because of the pore size reduction when the molecule size is comparable with the pore size along with the induced surface diffusion. Surface diffusion between the free gas phase and adsorption phase enhances gas permeability. Pore size reduction and the adsorption layer both have complex impacts on gas apparent permeability, plus the non-Darcy flow component make shale gas permeability look mysterious. These physical processes are difficult to couple with fluid flow, and previous research is generally incomplete. This work proposes a methodology to take these various effects into account simultaneously. Our results show that the geomechanical effect significantly reduces the intrinsic permeability of shale gas. However, slip flow and pore diffusion begin to overwhelm the geomechanical effect at reservoir pressure of 500 psi and below. As for the adsorption layer, it changes little of shale gas permeability but its induced surface diffusion might increase gas flow capacity significantly at low pressure, and the influence depends on the value of surface diffusivity. The workflow proposed in this study is considered to be useful to describe shale gas permeability evolution considering these physics together.

IMPROVEMENT OF HYDROCHLORIC ACID FORMATION TREATMENT FOR VOLGO-URALS CARBONATES

Background. At the present stage of development of the oil and gas industry, the structure of oil reserves in the Republic of Bashkortostan is deteriorating. The share of hard-to-recover oil reserves, including those associated with carbonate reservoirs, is increasing. More than 2 0 % of residual and hard-to-recover oil reserves of Bashkortostan are found in carbonate reservoirs. Productive deposits containing oil deposits have a complex geological structure. The development of these reserves will allow maintaining the current level of hydrocarbon production for a long time. The use of hydrochloric acid carbonate reservoirs treatment allows to increase the efficiency of exploitation of these deposits. However, oil deposits in carbonate reservoirs are often operated with an ineffective water flooding system or on a natural regime, which leads to a decrease in reservoir pressure in the bottomhole zone of producing wells. The use of standard hydrochloric acid treatment of production wells under these conditions proves ineffective. In this regard, studies have been conducted aimed at increasing the effectiveness of measures to intensify oil production, which, of course, is an urgent task. Aims and Objectives. Improvement of the hydrochloric acid treatment for Volga-Ural carbonate reservoirs in conditions of low reservoir pressure to increase the efficiency of the method of stimulation of the inflow to the wells. Metods. The mechanism of action of the acid solution on the productive reservoir is based on analytical methods of research. Determination of the rate of reaction of acid solutions with carbonate rock using reaction moderators and reagents is based on a generalization of the results of laboratory studies. Commercial types of research were used in experimental-industrial tests of the proposed method of hydrochloric acid exposure. The results of field work on the intensification of the inflow to production wells were processed using analytical and mathematical methods. Rezults. Based on the concept of the mechanism of the process of oil displacement from weakly permeable carbonate reservoirs, methods for treating the bottomhole zone of producing wells, including those for low reservoir pressure, are proposed. The results of the implementation of the proposed method made it possible to increase the production rate by more than 2 times in comparison with the treatment performed by traditional technology, and the duration of the effect from treatment was much larger. Conclusion. The application of the proposed methods of hydrochloric acid treatment during the intensification of the influx from the carbonate layers of the Bashkir and Vereiskian, Tournaisian stages, including for the conditions of low reservoir pressure in the Republic of Bashkortostan oil fields, will significantly improve the efficiency of the work.

Problems in the development of high-rank CBM horizontal wells in the Fanzhuang–Zhengzhuang Block in the Qinshui Basin and countermeasures

Coal reservoirs in the Qinshui Basin are characterized by high thermal evolution degree, low permeability, low reservoir pressure, lower gas saturation and strong heterogeneity, so its coalbed methane (CBM) development is quite difficult. In this paper, the development practice of high-rank CBM horizontal wells in the Fanzhuang–Zhengzhuang Block was analyzed in terms of geological and engineering factors to clarify the productivity influencing factors, suitable geological conditions and potential tapping countermeasures of multi-lateral horizontal wells. It is shown that the reasons for the low development efficiency of multi-lateral horizontal wells are divided into three types. The first one is geological factor, such as encountering low CBM content areas or faults. The second is engineering factor, such as drilling fluid plugging, drilling collapse, drainage collapse and dust coal blockage. The third is the combination of both factors. It is concluded that encountering low CBM content areas and faults, collapse and blockage are the main reasons for the low production of multi-lateral horizontal wells in the Zhengzhuang–Fanzhuang Block, with the CBM content higher than 20 m3/t, the ratio of critical desorption pressure and reservoir pressure higher than 0.7 and vitrinite reflectance (Ro) higher than 3.8. The prerequisite for an open-hole horizontal well in this area to produce CBM at a high rate is that the well lies in the tensile stress zone. Finally, the countermeasures to tap the potential of some inefficient wells were put forward. First, the inefficient wells which are blocked with dust coal or collapsed in the later stage should be stimulated based on classifications. And second, it is necessary to explore new types of horizontal wells so as to deal with borehole collapse and continue the operation in the later stage by using tree-like roof horizontal wells, single-lateral horizontal wells with casing or screen completion and fish-bone horizontal wells.

Numerical study of air assisted cyclic steam stimulation process for heavy oil reservoirs: Recovery performance and energy efficiency analysis

Cyclic steam stimulation (CSS) has been widely applied asan effective technique for heavy oil reservoirs, but it is increasingly concerned in recent years for its limited oil recovery performance, low energy efficiency, high water consumption and great environmental footprints due to greenhouse gas emissions. The hybrid injection of air and steam in terms of low temperature oxidation (LTO) is an innovative technique for the development of heavy oil reservoirs, which can be operated based on the conventional well configuration and was firstly proposed as an enhanced oil recovery (EOR) process for mature heavy oil reservoirs encountered with low reservoir pressure, poor steam sweep efficiency and high water cut. In this study, numerical simulation study is conducted to evaluate the potentials of air assisted cyclic steam stimulation (AACSS) process as an alternative to CSS technique for heavy oil reservoirs. Effects of oil viscosity, LTO reaction and operated air to steam ratio on the well performance are examined for typical heavy oils. The results indicate that AACSS process can effectively improve oil recovery, enhance the energy efficiency and reduce CO2 emissions in comparison with CSS alone, which can be attributed to the thermal effect due to oil oxidation, reservoir repressurization and gas driving offered by air injection, and the AACSS process can be more economically and environmentally attractive than CSS alone. The production performance of AACSS process for ultra heavy oil reservoirs can be more pronounced in comparison with that of ordinary heavy oils, and the LTO characteristics of different oils and the feasible air to steam ratio are reservoir specific for field operation.

How Will Subsea-Processing Technologies Enable Deepwater-Field Developments?

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 27661, “How Will Subsea Processing and Pumping Technologies Enable Future Deepwater-Field Developments?,” by Phaneendra B. Kondapi, Texas A&M University, and Y. Doreen Chin, Ashesh Srivastava, and Zuying F. Yang, Subsea Engineering Technologies, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. This study examines how subsea processing (SSP) can develop into an important enabling technology for future ultradeepwater-field developments and long-distance tiebacks. The authors identify the gaps that need to be closed and describe the decision-making process during the field-development life cycle by considering the technical and economic constraints of various SSP technologies. Introduction A generalized definition of SSP is any active treatment of the produced fluids at or below the seabed to improve recovery factor of reservoirs. SSP technologies include multiphase pumping, subsea separation, gas compression, and raw-seawater injection. Subsea separation coupled with liquid boosting is effective in enabling production at very low flowing tubinghead pressures, even in deep water. This method also is well-suited for use where heavy, viscous oil or low reservoir pressure is the rule. Gas fields often are developed with subsea wells and multiphase transport to onshore facilities or to offshore processing platforms. Separation allows decreasing boosting-power requirements. Subsea-separation technology is progressing quickly because of its huge potential in minimizing topside water-handling requirements and separation of gas, oil, and water from the production fluid. Subsea gas-compression technology is one of the faster-growing technologies for large fields requiring pressure boosting (e.g., where subsea-to-beach development solutions result in long tie-back distances). It improves the production and recovery from the reservoir by reducing backpressure on the wells. As of this writing, more than 25 subsea boosting systems and six major subsea separation systems have been installed or awarded throughout the world. Given the growing number of greenfield and brownfield applications, some analysts anticipate the number of SSP systems installed globally to double by 2020. The complete paper contains a detailed discussion of the development of these technologies, from their origins to their current incarnations. Why SSP? SSP is typically considered for systems with a tieback to a host structure and can influence all phases of project life (start-up, plateau production, late life, and tail end). SSP can consist of the following: Use of single- or multiphase pumping systems to enhance the fluid-driving energy (subsea boosting) Subsea separation and disposal of the produced water (two-phase separation) Subsea separation of oil, gas, and water (three-phase separation)

Exstrophy Bladder – Reconstruction or Diversion for the Underprivileged

The surgical techniques for management of bladder exstrophy epispadias complex have evolved from staged reconstruction, complete primary repair to radical mobilization. Post-operative complications add to the multiplicity of surgical procedures at each step. The end results are variable with many achieving continence rates of 85-89% only after bladder augmentation and clean intermittent catheterization. The situation is further complicated in resource-poor settings, where illiteracy and poverty are the driving factors for choosing a single operative procedure for creation of low pressure reservoir aiming at upper tract preservation and good primary continence. Thus, primary urinary diversion should be offered as a surgical option to patients with limited access to health care facilities. Yogesh's cystorectostomy is a modification of Heitz-Boyer-Hovelacque procedure, wherein the bladder plate is directly anastomosed to the recto-sigmoid pouch, without mobilizing the ureters from their original location. The short-term follow-ups are encouraging with all achieving total urinary continence over the ensuing months. The upper tract functions are well preserved, along with huge parental and patient satisfaction and overall improvement in the quality of life.

Novel Coiled-Tubing Perforation Technique and Stimulation in Carbonate Gas Well

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18880, “Novel Abrasive Perforating With Acid-Soluble Material and Subsequent Coiled-Tubing Jetting-Assisted Stimulation Provide Outstanding Results in Carbonate Gas Well,” by Adrian Buenrostro, Nahr Abulhamayel, Usman Malik, Mohammad Bu Suwaileh, and Saad Driweesh, Saudi Aramco, and Alejandro Chacon, José Camilo Jimenez Fadul, and José Noguera, Halliburton, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission. Abrasive perforating with coiled tubing (CT) is a technique that has proved to be a valuable alternative to conventional perforating with electric line. The application is particularly valuable whenever a high rate or fracture-stimulation treatment is to follow because of the significant reduction in tortuosity and pumping friction losses across perforations. This paper discusses a novel approach to abrasive perforating, including the first-ever use of an acid-soluble abrasive material and ending with CT-jetting-assisted nitrified stimulation. Introduction Many carbonate gas wells located in the northern section of the Ghawar reservoir exhibit a low-permeability profile and are characterized by having low reservoir pressure. Fracture gradients in a formation in this area of the field are on the order of 1.12 psi/ft, which is considerably greater than that of more-conventional tight gas formations. One particular well, located on the flank of the reservoir, was designed to be completed with a plug-and-perforate acid-fracturing operation, but issues arose with this option that finally caused the abandonment of the fracturing treatment. To find a solution that would be feasible and economically viable, an innovative perforation and stimulation technique was engineered for this well. Design of the Perforation Technique and Yard Testing The team was able to source a newly developed acid-soluble abrasive material that enabled the same quality of perforations to be created without performing a cleanout run because the acid from the stimulation would dissolve the abrasive material, saving at least 2 days of operation. The abrasive material was sourced, and several yard tests were completed to determine if the material had the same abrasive characteristics as common 20/40- or 100-mesh sand. It was necessary to compare the time required to penetrate the steel and cement with the results obtained using common sand. This benchmarking was key to determining if additional time and fluid resources were necessary to obtain the same penetration. A yard test was set up with two metallic 55-gal drums cut halfway lengthwise and then welded together. This created a receptacle that allowed the team to place a 6⅝-in. casing section with 100% standoff and then fill the entire annular space with cement. The drum was then set on top of cement blocks, and the abrasive-jetting tool was introduced.

Pressure Loss Estimation of Three-Phase Flow in Inclined Annuli for Underbalanced Drilling Condition using Artificial Intelligence

Underbalanced drilling as multiphase flow is done in oil drilling operation in low pressure reservoir or highly depleted mature reservoir. Correct determination of the pressure loss of three phase fluids in drilling annulus is essential in determination of hydraulic horsepower requirements during drilling operations. In this paper the pressure loss of solid-gas-liquid three-phase fluids flow in inclined annulus was estimated using artificial neural network (ANN). Experimental data which are available in the literature were used for design of ANN. Pressure loss as output of ANN, was estimated from five effective parameters as inputs of ANN including gas and liquid superficial velocities, the inclination from horizontal, rate of penetration (ROP), pipe rotation speed (RPM). The correlation coefficient between predicted and experimental value for train and test data is 0.998 and 0.997 respectively.The root mean square error (RMS) and average absolute percent relative error (AAPE) for train data are 0.0082 and 2.77% and for test data, they are 0.0108 and 3.68 % respectively. The reliable results showed the high ability of artificial neural network for estimating pressure loss of three phase flow in annulus.

An innovative air assisted cyclic steam stimulation technique for enhanced heavy oil recovery

Air assisted cyclic steam stimulation (AACSS) is an innovative technique for enhanced heavy oil recovery, in which air is injected along with steam injection during a conventional CSS process. It can be applied for heavy or ultra heavy oil reservoirs in the late stage of CSS process to increase the performance of steam injection and mitigate the problems of low reservoir pressure, poor steam sweep efficiency and high water cut. In this study, the application of the AACSS technique in a typical ultra heavy oil reservoir of Liaohe oilfield (China) was described and its field performances were analyzed along with a numerical reservoir simulation study to reveal its mechanism. The field data shows that the AACSS can significantly increase oil production, reduce water cut and prolong the effective production period. A reaction model for the oxidation of heavy oil components with oxygen in the temperature range of 50–300°C was established, based on the experimental results of thermogravimetric analysis (TGA), to simulate the conversion of air into flue gas and its thermal effect. The performance of AACSS was investigated and the contribution of thermal effect induced by LTO reactions was analyzed through numerical simulation. The simulation results indicate that air injection can improve oil recovery on the basis of CSS, in which over 11% of the incremental oil production can be attributed to the thermal effect, and the rest is accounted for a complex effect of flue gas driving.

Application of dynamic simulation to assess the effectiveness of well clean-up in a horizontal gas well

Well clean-up operation involves the removal of drilling and completion fluids from the wellbore before diverting the well to production facilities. Natural flow clean-up is preferred due to its relatively low cost and simplicity. Depending on the weight of the initial contents in the wellbore and the reservoir properties, artificial lift assisted clean-up such as nitrogen injection through coiled tubing may be required for some wells to ensure the well clean-up objectives are achieved. Well clean-up is transient in nature thus necessitating the need for a dynamic simulation approach to assess the effectiveness of different clean-up options and arrive at the optimal procedure before embarking on the actual field operation. In the current study, a comprehensive-multiphase-transient-simulator (OLGA) was used to predict the clean-up of a gas well with relatively short horizontal open-hole section and low reservoir pressure. Dynamic simulations of clean-up operations for different scenarios such as mud cake lift-off pressures and uncertainties in well productivity were conducted to assess the effectiveness of natural clean-up. Well clean-up failure could lead to impaired deliverability and potential for preferential flow hotspots. The study also assessed if coiled tubing-assisted operations would be beneficial in cases of natural clean-up being ineffective. This paper demonstrates the importance of using transient simulations to provide useful insights into flow and pressure dynamics inside the wellbore during clean-up which can help engineers to predict, design and optimise well clean-up operations, thus increasing the probability of a successful clean-up operation.

Underbalance well completion - a modern approach for mature gas fields

The exploitation of natural gas fields from Transylvanian Basin started a century ago. The majority of these fields were discovered and developed in the last century, from 1950 to 1970. So, these reservoirs have over 50 years of production historical. These are mature fields with a very low reservoir pressure. Now, for some of these reservoirs the pressure is 10 – 20 % of initial values. The biggest challenge for a production company is to make completions and recompletions in depleted reservoirs wells. At the beginning was not a problem to do a workover in these wells because the completion fluids were lost in the reservoir and the pressure helped the wells to clean up. Now, because the reservoir pressure is very low, it takes time for well to be cleaned. From time to time, some net pays have to be bypassed because the fluid can be lost in the reservoir. So the best method to do recompletion works in these wells is to work underbalance or even with the well under pressure. This paper presents some of the technologies used by Romgaz to accomplish this goal.

Анализ и обоснование выбора составов для ограничения водопритоков при заканчивании скважин

The aim of the work is to increase efficiency of well completion under conditions of water inflow by use of viscoelastic gas-liquid mixtures to shut-off permeable formations. At present, there is an increase in rates of drilling of wells in abnormal conditions, such as abnormal formation pressure (both low and high), unstable rocks, rocks of high hardness, permafrost etc. The quality of well construction in such conditions influences subsequent development and operation of the field greatly. Aquifer isolation is an extremely important issue due to the fact that from them water breaks through in production wells which has a significant impact on quality of fluid produced. The main solution for water breakthrough challenge is formation isolation, which is performed by use of various plugging material. At present, there are many mixtures that limit water inflows such as fast-setting plugging materials, gel-cement mixtures, polymeric swelling nets, latexes, synthetic resins, viscoelastic mixtures, materials for selective isolation etc. Under conditions of abnormally low reservoir pressures, it is important to consider density when selecting drilling fluids and plugging materials. Therefore, it is recommended to use screens based on viscoelastic three-phase stabilized gas-liquid mixtures for temporary blockage of permeable aquifer. With use of such mixtures liquid penetration flow rate is significantly reduced compared to other viscoelastic systems, which makes it possible to increase reliability of temporary isolation of aquifers. The paper presents an analysis of domestic and foreign experience of blocking permeable formations by different mixtures. Three-phase blocking mixtures are studied and requirements for them are generalized.

Preperitoneal Bladder Augmentation: Feasibility and Results.

Introduction:Bladder augmentation is an important part of pediatric reconstructive urology. This study was conducted to assess the feasibility and results of our technique of preperitoneal bladder augmentation.Materials and Methods:Thirty-three children underwent preperitoneal bladder augmentation for small inelastic bladders who had failed medical management or needed undiversion. The underlying diagnosis included neurogenic bladder, valve bladder, bladder exstrophy, non-neurogenic neurogenic, ectopic ureters, and urogenital sinus. The operative procedure involved placing the entire augmentation in the preperitoneal or subcutaneous space after bivalving the native bladder. The augment segment of the bowel with its pedicle was brought into the preperitoneal space through a small opening in the parietal peritoneum. A Mitrofanoff port was also provided where needed.Results:Preperitoneal augmentation provided an adequately compliant, good volume bladder except in children with bladder exstrophy or previous abdominal surgery. There was a good cystometric recovery, with resolution of hydronephrosis and incontinence. Vesicoureteral reflux resolved in 24 of 26 units. In the 13 children who were uremic preoperatively, there was a significant decrease in serum creatinine levels, although 9 children continued to have supra-normal serum creatinine. Surgical complications seen were within expectations. There was no incidence of intraperitoneal leak, which is the main projected benefit of this procedure over the traditional “intraperitoneal” method of augmentation.Conclusions:The preperitoneal augmentation provides an adequate, safe, and low-pressure reservoir of urine except in cases of bladder exstrophy and previous abdominal surgery.

Estimation of Pressure-Dependent Diffusive Permeability of Coal Using Methane Diffusion Coefficient: Laboratory Measurements and Modeling

Gas diffusion in coal is critical for the prediction of coalbed methane (CBM) production, especially for the late-stage CBM reservoir when both gas pressure and permeability are relative low. Using only Darcy permeability to evaluate the quality of gas transport might not be effective. Diffusive flow can be the dominant flow at low reservoir pressures. In this work, the methane diffusion coefficient was measured for pulverized San Juan sub-bituminous and Pittsburgh bituminous coal samples using the classic unipore model and particle method. The diffusion coefficient results showed a negative correlation with pressure, as reported previously. The significance of diffusion flow is strongly related to the rate of the methane ad-/desorption process, more severely in the low pressure range [<2 MPa (280 psi)]. The measured diffusion coefficient can be converted to the equivalent permeability. This equivalent permeability, termed diffusive permeability, can be considered as the contribution of diffusion flow, in...

Phase behavior and flow in shale nanopores from molecular simulations

Phase behavior and flow in shale nanopores, due to fluid heterogeneity, cannot be described by bulk and continuum-based formulations. The interactions between fluid and rock molecules are important in both phase behavior and flow. As a result, frameworks from bulk equations of state in phase behavior, and continuum mechanisms and Klinkenberg slippage in flow may become inapplicable. Recently, we have studied both phase behavior and flow in nanopores using density functional theory and various molecular simulations. This work addresses a number of issues related to the adsorption of mixtures of hydrocarbons, carbon dioxide and water as well as methane flow at different pressure conditions in nanopores. For flow, we use the dual control volume-grand canonical molecular dynamics (DCV-GCMD) simulation as in our previous work. We use a smaller pressure difference between high and low pressure reservoirs connected to the nanopores. We find that similar to our past work, the flux of methane in the slit pores can be two orders of magnitude higher than the results from the Hagen-Poiseuille equation.

Characteristics and resource prospects of tight oil in Ordos Basin, China

AbstractEfficient large-scale development of ultra-low-permeability reservoirs (0.3–1mD) has been achieved in the Changqing Oilfield, Ordos Basin of China. According to unique features of petroleum exploration and development in this basin, tight oil herein refers to petroleum that occurs in oil-bearing shales and interbedded tight sandstone reservoirs adjacent to source rocks with ambient air permeability <0.3mD. Tight oil in tight sandstone and shale have generally not yet experienced large-scale long-distance migration. In the Yanchang Formation, tight oil has mainly accumulated in the semi-deep to deep lacustrine facies, typically in oil-bearing shales and tight sandstones of the 7th member oil-bearing formation and tight sandstones of the 6th member oil-bearing formation in the center of the basin. Tight oil resource in the Ordos Basin is characterized by wide spatial distribution, excellent source rocks, extremely tight sandstone reservoirs, complex pore throat structures, poor physical properties, high oil saturation, good crude-oil properties, and low reservoir pressure. A fundamental feature of the continuous oil and gas accumulation in tight oil reservoirs is the widespread development of nano-scale pore-throat systems. In the Yanchang Formation, most of connected pore throats in tight sandstone reservoirs have diameters greater than critical pore throat diameter, allowing oil and gas migration in the tight reservoirs. According to contact relationship between tight reservoirs and source rocks, three types of tight oil reservoirs are identified in the Yanchang Formation, i.e., tight massive sandstone reservoir, sand - shale interbed reservoir, and oil-bearing shale reservoir. In the Ordos Basin, tight oil is widely distributed in the 6th and 7th members of the Yanchang Formation, with total resources estimated to be 3×109 t. These include > 1×109 t of oil resources in shale in the 7th member of the Yanchang Formation and approximately 0.9×109 t and 1.1×109 t of tight sandstone oil resource in the 6th and 7th members of the Yanchang Formation, respectively. These tight oil resources are the realistic resources addition for the oilfield, which can ensure an annual production of 50×106 t of oil and gas equivalent and maintain long-term stable oil production in the Changqing Oilfield, Ordos Basin, China.

Control of a hydraulic regenerative braking system for a heavy goods vehicle

This paper investigates the fuel consumption of an articulated vehicle with a hydraulic regenerative braking system. The vehicle is a four-axle tractor–semitrailer with a volume-limited payload. It is equipped with hub-mounted hydraulic pump–motor units that pump fluid from a low-pressure reservoir to a high-pressure reservoir during braking events and generate a propulsive torque when high-pressure fluid flows through them to the low-pressure reservoir during acceleration. Several possible control strategies are proposed and simulated using a validated mathematical model of the fuel consumption of the vehicle. A global optimisation calculation indicates that the maximum possible reduction in fuel consumption due to the regenerative braking system is 11–22%, depending on the driving cycle. The simulations indicate that the simple ‘greedy’ algorithm decreases the fuel consumption by 9–17% for the same conditions. Two heuristic algorithms and a model predictive control approach were also investigated. Although these more sophisticated controllers were able to improve on the greedy controller slightly for some conditions, they may not be implementable in practice.

Factors Controlling Fluid Migration and Distribution in the Eagle Ford Shale

Summary Production of shale and tight oil is the cornerstone of the United States race for energy independence. According to the US Energy Information Administration, approximately 90% of the oil-production growth comes from six tight-oil plays. The Eagle Ford is one of these plays, and it accounts for 33% of the oil-production growth with a contribution of 1.3 million B/D. This is outstanding. However, oil recoveries as a percentage of the original oil in place (OOIP) are extremely low. This must be improved. A geological challenge in the Eagle Ford shale is the understanding of unconventional fluids distribution over geologic time: Shallower in the structure, there is black oil; deeper and to the south; condensate appears; and at the bottom, dry gas can be found. Differences in burial depth, temperature, and vitrinite reflectance are used to explain this unique distribution. A similar fluid distribution occurs in other unconventional reservoirs (e.g., Duvernay shale in Canada). The low oil recovery and the unusual distribution of fluids led to the key objective of this paper—to identify the main factors that control fluid migration (caused by buoyancy of gas in oil) from one zone to another through geologic time. This was performed by constructing a conceptual cross-sectional compositional simulation model with northwest/southeast orientation that allowed the study of fluid migration, fluid distribution, and fluid contacts throughout 1 million years while maintaining computational time within reasonable limits. The controlling parameters studied were porosity, permeability, pore-throat aperture (rp35), and spacing between natural fractures. Results show that fluids in the matrix remained with approximately the same original distribution (i.e., approximately the same dry-gas/condensate contact and approximately the same condensate/oil contact). These fluids are the target of an ongoing research project with the ultimate goal of improving oil recovery from tight reservoirs by means of enhanced oil recovery (EOR) (Fragoso et al. 2015). There is, however, some gas migration through natural fractures to the top of the structure. This migration is interpreted in this study to be responsible for higher initial gas production in some oil wells in the top of the structure. Some operators indicate, however, that rapid gas/oil-ratio increases in the updip oil region are the result of low reservoir pressures and the rapid onset of two-phase flow. It would probably take geochemical evidence to support this conclusion.

SPECIFICS OF KILLING THE WELLS WITH A LEAKY PRODUCTION STRING

In this paper a method is presented for gas and gas condensate wells killing in the complicated conditions, that is in the conditions of abnormally low reservoir pressures and with presence of casing string leaks.

Long-term Functional, Urodynamic, and Metabolic Outcome of a Modified Orthotopic Neobladder Created With a Short Ileal Segment: Our 5-year Experience

To assess the long-term functional, urodynamic, and metabolic outcomes of our modified neobladder. In this prospective study from January 2010 to October 2014, 42 consecutive male patients with bladder tumor underwent radical cystectomy and orthotopic urinary diversion with modified ileal neobladder using 25 cm ileal segment. During follow-up, functional outcome, urodynamic studies, metabolic parameters, and renal parameters were assessed at regular intervals. Complications were graded as early (<3 months) or late (>3 months). There were no perioperative deaths. At a mean follow-up of 27.2 months, good or satisfactory daytime and nighttime continence were achieved in 100% and 93.8% of patients, respectively. Mean maximal bladder capacity was 588 mL at 3 years. Mean resting pressure and voiding pressures were 20.1 cm H2O and 34.6 cm H2O at 3 years, respectively. Good bladder compliance was achieved in all patients by 1 year. Mean maximum urine flow rate (Qmax) was 18.5 mL at 3 years. Postvoid residual volume was insignificant in all the patients and none of the patients were on clean intermittent self-catheterization. None of the patients developed severe metabolic acidosis. Vitamin B12 levels were within normal range in all patients. Early complications were seen in 12 patients (28.6%), whereas late complications were observed in 5 patients (12%). Our results demonstrate that our modified technique of using a short ileal segment to create a near-spherical, compliant, low-pressure reservoir provides an acceptable, safe, and functional alternative to the standard Hautmann neobladder.