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Yang, Xiaoling (CNPC Daqing) | Qiu, Bilan (CNPC Daqing) | Qi, Dunke (CNPC Daqing) | Lv, Deqing (CNPC Daqing) | He, Jian (CNPC Daqing) | Zhou, Shubo (Halliburton) | Wang, Zichao (Halliburton) | Han, Rong (Halliburton)
Abstract A case study is presented discussing a specific completion strategy applied in the Daqing oil field, Block Long26, and the outskirts of tight oil wells. An alternative fracture completion method and enhanced flowback technology were used to develop these tight oil fields. The methodology applied resulted in improved efficiency of the fracture completion strategy and post-stimulation flowback, which reduced operational time and related costs. Optimized fracture cluster spacing length was determined based on the operational time efficiency and engineered fracture completion design. Laboratory testing was performed to select fluid recipes, and field trials were performed for the correlated custom-made microemulsion technology, which enhanced post-fracture flowback to shorten operational time and increase the return on investment ratio and production. Field results and post-fracture completion production are promising. Several post-fracture completion production surveys have been applied in the Daqing field, Block Long26. The most popular completion strategy applied in this field involves using less than three perforation clusters in each fracture stage, applied using multiple, horizontal fracture stages, with longer and (normally) much greater fracture spacing length, thus requiring less fracture cluster treatments along the horizontal laterals. After stimulation, normally, additional days are necessary to observe the oil drop showing; thus, alternative flowback technology is necessary to enhance post-stimulation flowback to help improve the return on investment ratio. Limited entry fracture and/or extreme limited entry fracture technology were part of the intensive fracture cluster completion strategy to benefit fracture completion and production. Field operations involved doubling the current perforation and fracture clusters in one fracture stage. Laboratory methods were used to select the appropriate mircoemulsion additives to form a fracturing fluid recipe to aid oil production and enhance flowback.
Huckabee, Paul (Shell Exploration & Production Co.) | Ledet, Chris (Shell Exploration & Production Co.) | Ugueto, Gustavo (Shell Exploration & Production Co.) | Tolle, John (Shell Exploration & Production Co.) | Mondal, Somnath (Shell Exploration & Production Co.)
Abstract This paper presents design considerations and field trial applications for determining practical dimensions and limits for interdependencies associated with stage length, perforation clusters and limited entry pressures. Recent applications by multiple authors and companies have begun to reverse the decade-long trend of reducing stage length and perforation spacing, in favor of extending stage lengths, to capture free cash flow value for unconventional resource development. Aggressive limited entry has been an enabler for successful extended stage length applications. Multiple authors have advocated "eXtreme Limited Entry" (XLE) applications. We present diagnostics data and applications that challenges the need for XLE and better constrains the necessary amount of limited entry pressures for effective stimulation distribution for resource development across multiple North American Basins. Data is presented from integrated application of field trials, stimulation distribution diagnostics, and well performance analysis. Field trials and well performance analysis are from the Permian Delaware Basin Wolfcamp. The field trials include both: greater perforation cluster intensities for base design stage lengths; and extended stage lengths of 50% greater than the base designs. Diagnostics are from multiple North American Basins and include discrete treatment pressure diagnostics and optic fiber distributed sensing. Data is presented to quantify the magnitude and variability for components necessary for maintaining active fracture extension for multiple perforation clusters. Components include: fracture breakdown pressures; in-situ stress, net fracture extension pressure, and near wellbore complexity pressure drop. Data and examples are presented from multiple wells, and resource development areas, to show the variability in measured treatment pressures for different length scale dimensions. This variability is used to determine the amount of limited entry pressure required to maintain fracture extension, dependent on the stage length dimension. Although Aggressive Limited Entry (ALE) is generally required to enable effective stimulation distribution and extended stage lengths in multiple cluster stages, examples are presented that demonstrate XLE is generally not required. We also discuss some of the considerations and observations that limit perforation cluster spacing intensities. Well performance data from the field trials is presented to validate the applications. This work demonstrates the value of integrated application of field trials, stimulation distribution diagnostics, and well performance analysis to capture free cash flow value from improved completions and stimulation designs. The discussion will include an assessment of future opportunities for further extension of stage length dimensions.
Abstract Historical horizontal completions designs have very wide cluster spacing, leaving behind significant volumes of hydrocarbons. This paper develops a workflow for optimizing cluster spacing using simulated production curves in unconventional oil and gas fields. Optimizing cluster spacing reduces unstimulated reservoir rock left between widely spaced fractures, more efficiently draining the stimulated reservoir volume and increasing expected ultimate recovery and initial production. This paper illustrates the workflow developed by finding an optimal range for cluster spacing in the retrograde/wet gas region of the Eagle Ford. It is estimated that optimizing cluster spacing in this fluid window will increase ultimate hydrocarbon recovery by 20% and the net present value of each well by 50-60%.
Through near 3000 horizontal producing wells on University Lands in the Permian Basin, we have performed a series of case studies to systematically investigate the most critical parameters to maximize well performance and the value of field development. In addition to summarizing multiple study results, the paper concludes and elaborates that the effective cluster spacing is the most critical parameter that we may be able to control and can influence the most in the unconventional reservoir development.
The paper first shows three observation cases of perforation cluster spacings and their corresponding well performance. To understand why the effective cluster spacing is so vital to well performance, we then illustrate the fundamental theory to understand the pressure propagation timing and depletion patterns in different reservoirs. We compare the mechanistic modeling results of pressure depletion and corresponding recovery efficiencies with different effective cluster spacings by multiple modeling approaches, including single-porosity model, and dual-porosity model, which has validated our case study results and is very insightful for us to optimize perforation cluster spacings.
We then discuss the possible reasons of often-observed well interference. With a large data sample, the paper illustrates the good correlation between well performance and completion effectiveness. The paper presents the EUR and NPV evaluation results of different field development case histories, such as between tight cluster spacing and wide cluster spacing. We will also briefly discuss the current technologies and practices to improve cluster efficiency in the completion process.
Based upon the multiple case studies, theory investigation, and rigorous modeling, we have concluded that the effective cluster spacing is the most critical factor to influence well performance and the field development value.
The workflow illustrated in the paper can be used for operators to systematically optimize their cluster spacings as well as field development plans. To maximize the value of developing unconventional reservoirs, it is vital to optimize cluster spacing and cost-effectively achieve tighter effective cluster spacing.
Abstract A major outstanding challenge in developing unconventional wells is determining the optimal cluster spacing. The spacing between perforation clusters influences hydraulic fracture geometry, drainage volume, production rates, and the estimated ultimate recovery (EUR) of a well. This paper systematically examines the impact of cluster spacing in the Eagle Ford shale wells by calibrating fracture geometry and fracture/reservoir properties using field injection and production data and evaluating the optimal cluster spacing under different reservoir conditions. We explore a sequential technique to evaluate and optimize cluster spacing using a controlled field test at the Eagle Ford field. This study first identifies the fracture geometry by history matching the field injection treatment pressure. Using the rapid Fast Marching Method based flow simulation and Pareto-based multi-objective history matching, we match the well drainage volume and the cumulative production to calibrate the fracture and SRV properties. The impact of cluster spacing on the EUR are examined using the calibrated models. We run injection and production forecasts for various cluster spacing to investigate optimal completion under different reservoir conditions. The unique set of injection and production data used for this study includes two horizontal wells completed side by side. The well with tighter cluster spacing has larger drainage volume and better production performance. This is because of the increased fracture complexity in spite of the impact of stress shadow effects leading to shorter fractures. The calibrated models suggest that most of the fractures are planar in the Eagle Ford shale. The well with wider cluster spacing tends to develop longer fractures but the well with tighter cluster spacing has better stimulated reservoir volume with enhanced permeability, thus resulting in better drainage volume and production performance. From the optimization runs under different reservoir conditions, our results seem to indicate that when natural fractures are present or when stress anisotropy is high with no natural fractures, the wells with tighter cluster spacing tend to outperform the wells with wider cluster spacing. However, severe stress shadow effect is observed when stress anisotropy is low with no natural fractures, likely making tighter cluster spacing wells less favorable. The calibrated fracture geometries and properties with a unique set of Eagle Ford field data explain the performance variation for completions using different cluster spacing within the reservoir and provides insight into optimal cluster spacing under different reservoir conditions (low vs high stress anisotropy and with/without natural fractures).