Shale gas well productivity potential evaluation based on data-driven methods: case study in the WY block

Evaluating the productivity potential of shale gas well before fracturing reformation is imperative due to the complex fracturing mechanism and high operation investment. However, conventional single-factor analysis method has been unable to meet the demand of productivity potential evaluation due to the numerous and intricate influencing factors. In this paper, a data-driven-based approach is proposed based on the data of 282 shale gas wells in WY block. LightGBM is used to conduct feature ranking, K-means is utilized to classify wells and evaluate gas productivity according to geological features and fracturing operating parameters, and production optimization is realized through random forest. The experimental results show that shale gas productivity potential is basically determined by geological condition for the total influence weights of geologic properties take the proportion of 0.64 and that of engineering attributes is 0.36. The difference between each category of well is more obvious when the cluster number of well is four. Meanwhile, those low production wells with good geological conditions but unreasonable fracturing schemes have the greatest optimization space. The model constructed in this paper can classify shale gas wells according to their productivity differences, help providing suggestions for engineers on productivity evaluation and the design of fracturing operating parameters of shale gas well.

Corrosion behavior of 2205 duplex stainless steel in acidizing stimulation solution for oil and gas wells at 200°C

Purpose This paper aims to analyze the high temperature (200°C) corrosion behavior of 2205 duplex stainless steel in acidizing stimulation solution containing hydrochloric acid (HCl) and acetic acid. Design/methodology/approach The corrosion rate of 2205 duplex stainless steel in all kinds of acid solutions was calculated through immersion tests and electrochemical test. The corrosion product composition is analyzed by X-ray diffraction analysis. The element composition and element distribution before and after corrosion were analyzed by an X-ray energy spectrometer. The corrosion morphology of the steel surface was observed by a scanning electron microscope. Both static and dynamic corrosion experiments were carried out at 200°C. Findings The results show that 2205 duplex stainless steel has excellent corrosion resistance in low to high concentration acetic acid solutions, but increasing the concentration of Cl− in acetic acid solution will accelerate the corrosion rate. Low concentration HCl solution can cause serious corrosion to 2205 duplex stainless steel. The system of HCl and acetic acid will produce a synergistic effect on corrosion of 2205 duplex stainless steel and accelerate the corrosion. Sb2O3 is a good corrosion inhibitor synergist for high-temperature acidizing stimulation solution. Originality/value The amount of HCl that is used in acidizing stimulation is usually determined by the dissolution effect of the acid on the rocks, but for ultra-high-temperature reservoirs, the amount of HCl should be based on reducing the corrosion of oil and gas wells.

The First Behind-Casing Fiber-Optic Installation in a High-Pressure High-Temperature Deep Gas Well in Oman

This paper discusses the first fiber-optic (FO) installation in a vertical high-pressure high-temperature deep gas well in PDO, Oman. A specially designed fiber-optic cable was successfully installed and cemented behind the production casing, which was subsequently perforated in an oriented manner without damaging the cable. This paper also describes how the fiber-optic cable was used afterwards to acquire Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) data for the purpose of hydraulic fracturing diagnostics. Fiber-optic surveillance is becoming an increasingly important activity for well and reservoir surveillance. The added complexity of the fiber-optic installation will affect the well design, which is one of the elements that requires focused attention, especially when the fiber is installed behind casing. The impact on casing design, wellhead design, perforation strategy, and logging requirements will all be discussed. In order for a well to be completed with a permanent fiber-optic cable, a few critical procedures need to be followed, including: –modifying the wellhead design to include feedthrough ports for the cable;–optimizing the cement design;–imposing strict procedures to ensure the cable is installed behind the casing without getting stuck;–changing the perforation phasing to avoid damaging the cable;–mapping the location of the cable to allow the gun string to be oriented away from the cable. The fiber-optic cable itself needed to be designed to be protected in such a way that it would not be damaged during installation and completion (perf/frac) activities. Furthermore, the cable was also optimized to improve its detectability, to aid the oriented perforation. In deep gas wells, much more than in conventional shallow water injectors or oil producers, the well integrity aspect should be given special attention. Specifically, any risks related to unwanted gas leaks, either through the control line, poor cement, or because of other design errors should be avoided. In deep gas wells, high temperature and pressure will also play a big role in the expected lifespan of the cable. Finally, the well was hydraulically fractured in four stages, using the "plug-and-perf" technique, during which DAS and DTS data were acquired continuously and across all depths of the well. The data provided valuable information on the effectiveness of each of the frac stages, it could be used to analyze screen-outs and detect out-of-zone injection, and recommendations for the optimizations of future hydraulic frac designs could be derived. The fiber-optic data were also integrated with other open-hole data for improved understanding of the reservoir performance. The next step will be to acquire repeated time-lapse DAS and DTS data for production profiling, to gain more insights of how the long-term production performance is affected by the hydraulic frac operations.

An Optimization-Based Method for the Explicit Production Data Analysis of Gas Wells

This work aims at the exploration of production data analysis (PDA) methods without iterations. It can overcome limitations of the advanced type curve analysis relying on the iterative calculation of material-balance pseudotime and current explicit methods reckoning on specific production schedule assumptions. The dynamic material balance equation (DMBE) is strictly proved by the integral variable substitution based on the gas flow equation under the boundary dominated flow (BDF) condition and the static material balance equation (SMBE) of a gas reservoir. We introduce the pseudopressure level function γ(p) and the recovery factor function R(p) to rewrite the DMBE in terms of observed variable Y and estimated variable Ye; then the PDA can be transformed into an optimization problem of minimizing the error between Y and Ye. An optimization-based method for the explicit production data analysis of gas wells (OBM-EPDA), therefore, is developed in the paper, capable of determining the BDF constant and gas reserves explicitly and accurately for variable rate and/or variable flowing pressure systems. Three stimulated cases demonstrate the applicability and validity of OBM-EPDA with small errors less than 1% for estimated values of both reserves and Y. Not second to previous studies, the field case analysis further proves its practicability. It is shown that the nonlinear relation of γ to R can be represented by a polynomial function merely dependent on the inherent properties of the gas production system even before sorting out the production data. The errors of observed variable Y provided by OBM-EPDA facilitate the data quality control, and the elimination of outliers not subject to the BDF condition improves the reliability of the analysis. For various gas systems producing whether at a constant rate, a constant bottomhole pressure (BHP), or under variable rate and variable BHP conditions, the proposed method gives insights into the well-controlled volume and production capacity of the gas well whether in a low-pressure or high-pressure gas reservoir, where the compressibilities of rock and bound water are considered.

Review of studies on plugging compositions creation with controlled rheological properties and the ability to restore fluidity for completion, workover and abandonment of oil and gas wells

The main purpose of cementing oil and gas wells is zonal isolation of the formations exposed by the wellbore. During the entire life of the well, there should be no uncontrolled hydraulic communication between the developed formations and the surface, regardless of the composition and type of fluid (water, oil or gas). During the operation of the well, in addition to constant static ones, the casing and cement stone also experience various dynamic loads. The article presents an up-to-date review of experimental studies on the modification of grouting compositions and cement composites capable of autonomous selfhealing due to the introduction of various additives and nanomaterials. Such modification technologies significantly increase the tightness and resistance of cement to the effects of dynamic loads, the integrity of the cement stone. As a replacement for traditional cement materials, the authors propose the creation of grouting compositions with controlled physical and mechanical properties and the possibility of their re-liquefaction under the influence of temperature on the basis of bitumen or bitumen composites. Keywords: well plugging and abandoning; self-healing materials; autonomous self-healing; casing durability; impermeability of the cement stone; self-healing cement; bitumen and bitumen composites.

Study of Compositions for Selective Water Isolation in Gas Wells

A hydrophobic composition containing water repellents and highly volatile solvents is shown in this study to isolate water from the bottomhole formation zone of gas wells and reduce as much as possible the saturation of pore spaces with water. During injection, this composition shows selectivity and mostly penetrates water-saturated porous media. The study shows that the injection of such composition into porous media has a high water-insulating effect, reducing the water permeability of water-saturated porous media by 35 times with a degree of water isolation of 97%. Moreover, while injecting, it has selective action, mainly penetrating water-saturated media rather than gas-saturated media. As a result of injecting 0.91 to 0.99 pore volumes (pv) of the composition, the Qwater/Qgas ratio reaches 5.22 to 5.26, indicating high selectivity.

Analysis of the financial assurance problem for decommissioning of oil and gas wells and facilities

The harmful effects of oil and gas projects on the environment are not limited to the production period. Unlike operating production facilities, control over the state of abandoned wells and fields falls on the state. In the Russian Federation, the obligations of subsoil user companies to properly perform decommissioning operations are not legally regulated and financially secured. Based on world experience, the paper analyzes the most common schemes for formation and accounting of financial assurance for decommissioning operations and examines the state of legislative regulation on this problem in Russia and the world. It presents recommendations on state regulation to guarantee full completion of decommissioning operations by subsoil users, improve their quality and monitor the environmental safety of abandoned wells.

Numerical Simulation Research on Influencing Factors of Post-Fracturing Flowback of Shale Gas Wells in the Sichuan Basin

The horizontal well multistage hydraulic fracturing technology is the most effective way to exploit shale gas resources. Compared with conventional reservoir fracturing, the flowback rate of a fracturing fluid in a shale reservoir is extremely low, and a large amount of fracturing fluid remains in the formation. Therefore, the research on the mechanism of shale reservoir fracturing fluid flowback process will contribute to laying a theoretical foundation for improving the effect of the innovation for increasing output of shale gas wells. Based on the shale in the Sichuan Basin, this study first describes basic experiments on physical properties such as the porosity, permeability, mineral composition, wettability, and microstructure. The physical properties of shale reservoirs were also analyzed, which laid the foundation for subsequent modeling. Second, CMG software is used to establish a numerical model that fits the characteristics of the flowback process. The effect of reservoir properties, fracturing parameters, drainage–production system, chemical permeability on gas and water production in the flowback process and their mechanisms are also analyzed. According to most numerical simulation results, the lower cumulative gas production will be with the higher cumulative water production which means the higher flowback rate. The pursuit of only a high flowback rate is not advisable, and the development of the drainage–production system requires reasonable control of the fracturing fluid flowback rate. This study provides a theoretical basis for the optimization of shale gas drainage–production system after hydraulic fracturing.