Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Summary Hydraulic fractures propagate perpendicular to the horizontal-well axis whenever the drilling direction is parallel to the minimum-principal-stress direction. However, operators frequently drill horizontal wells parallel to lease boundaries, resulting in hydraulic-fracture vertical planes slanted at angles less than 90° from the well axis. The stimulated-rock-volume (SRV) dimensions are defined by fracture height, well length, and fracture length multiplied by the sine of the angle between fracture planes and the horizontal-well axis (fracture angle). The well productivity index (PI) under boundary-dominated flow (BDF) is given by the PI for one fully penetrating fracture multiplied by the number of fractures. An extension of the unified-fracture-design (UFD) approach for rectangular drainage areas enables determination of the unique number of fractures that will maximize well productivity under BDF conditions given the formation permeability, proppant mass, fracture angle, and well spacing. Fracture length and width vary depending on the fracture angle, but the total-propped-fracture volume remains constant. Because the likely reason for drilling at an angle to the minimum-stress direction is to better cover a lease area with north/south and east/west boundaries, the smallest fracture angle will be 45°, corresponding to northwest/southeast or northeast/southwest minimum-stress direction. This results in the need to lengthen fractures by at most 40% to preserve the SRV for a given horizontal-well length and spacing. For the same sufficiently large proppant mass, this will reduce fracture conductivity by the same factor. However, because the flow area has increased, the result will be greater well productivity. This study shows a simple strategy for designing wells to maximize productivity even when not drilled in the minimum-stress direction.
Summary Hydraulic fractures propagate perpendicular to the horizontal-well axis whenever the drilling direction is parallel to the minimum-principal-stress direction. However, operators frequently drill horizontal wells parallel to lease boundaries, resulting in hydraulic-fracture vertical planes slanted at angles less than 90° from the well axis. The stimulated-rock-volume (SRV) dimensions are defined by fracture height, well length, and fracture length multiplied by the sine of the angle between fracture planes and the horizontal-well axis (fracture angle). The well productivity index (PI) under boundary-dominated flow (BDF) is given by the PI for one fully penetrating fracture multiplied by the number of fractures. An extension of the unified-fracture-design (UFD) approach for rectangular drainage areas enables determination of the unique number of fractures that will maximize well productivity under BDF conditions given the formation permeability, proppant mass, fracture angle, and well spacing. Fracture length and width vary depending on the fracture angle, but the total-propped-fracture volume remains constant. Because the likely reason for drilling at an angle to the minimum-stress direction is to better cover a lease area with north/south and east/west boundaries, the smallest fracture angle will be 45°, corresponding to northwest/southeast or northeast/southwest minimum-stress direction. This results in the need to lengthen fractures by at most 40% to preserve the SRV for a given horizontal-well length and spacing. For the same sufficiently large proppant mass, this will reduce fracture conductivity by the same factor. However, because the flow area has increased, the result will be greater well productivity. This study shows a simple strategy for designing wells to maximize productivity even when not drilled in the minimum-stress direction.
North American unconventional well completion design has evolved dramatically since 2013 in an effort to keep pace with the productivity gains realized in horizontal drilling. Several trends have emerged during the current industry downturn. Among these trends are a focus on core acreage with higher yield potential, the use of longer laterals, a movement towards higher proppant loading (pounds per linear foot), an increased reliance on plug and perf techniques, and decreased stage length and perforation cluster spacing (increased perf density). As a result associated improvements in well initial production (IP) rates and estimated ultimate recoveries (EUR's) have been highlighted in oil & gas operator's quarterly shareholder's reports during 2015 and early 2016. Unconventional multi-stage completion designs have also quickly evolved along a path paralleling these trends. Horizontal well IP rates and EUR's have also been enhanced through the adoption of integrated completion designs. Recently introduced geo-engineered completions rely on cross-functional expertise and software to integrate petrophysical, geomechanical, drilling, and production data into a completion design. In cases where geo-engineered designs were used, wells showed improvements in EUR's over those associated with increased lateral lengths, proppant loading and stage counts. In one recent case using a geo-engineered design it was demonstrated that fewer stages and clusters achieved higher production than offset wells while injecting less proppant and fluid; thus achieving lower completion cost. The use of engineered workflows in tight or unconventional reservoirs is not new. Multiple case histories have been published in recent literature illustrating the use of stress variability/contrast or mechanical specific energy (MSE) to generate brittleness or other fraccability indices to group stages with similar rock characteristics. In contrast to engineered designs, newer geo-engineered designs integrate multiple inputs (attributes) to determine basin and formation-specific weighted algorithms that correlate to stage and cluster production contribution improvement. The geo-engineered approach has proven repeatable and can be accomplished even when key wireline or LWD data is not available. This paper will document how geo-engineered completion designs evolved from engineered workflows. Multiple inputs (e.g. production, wireline/LWD/mud logs, core analyses, and big data from national and state data bases) can be combined to determine stage length and perforation cluster positioning. Case studies will demonstrate that geo-engineered horizontal completion designs deliver superior well production results when compared to geometric, high-intensity plug & perf designs.
In the age of artificial intelligence, digitalization, rising energy demand, falling prices of barrel of oil and increasing difficulty in oil & gas recovery we need to have an integrated approach based on physics, artificial intelligence and rock mechanics to reduce the non-productive time in drilling and -in parallel- enhance well production. The integrated approach should help in reducing cost, minimize human intervention, reduce drilling associated risks, minimize the negative impact on near wellbore rock behavior due to stimulation and enhance the recovery of hydrocarbons. Stuck pipe is a major stake holder in "non-productive time" and is estimated to cost the oil and gas industry around $250 to $300 Million a year. Stuck pipe due to wellbore stability issues is a regular phenomenon while drilling weak zones in minimum stress direction especially in Middle East. William Lyon's in 2010, estimated that cost of stuck pipe in deep oil and gas wells is around 25% of overall budget. To counter stuck pipe, for instance, drilling engineer may decide to increase the mud weight inorder to minimize the wellbore stability issues, and this could enhance challenges to a stimulation engineer associated with potential damage. Simliarly, an improper acidizing could soften the rock and negatively impact mechanical response of near wellbore rock during production. Two simple examples demonstrate the value of an engineering holistic approach based on wellbore stability integration into hydraulic fracturing treatment design considering the complexity involved around geomechanics. This study introduces a workflow that holistically integrates a rock mechanics approach to optimize drilling performance and characterize the stresses around the wellbore with the completion design, combining the geomechanical and petrophysical properties to optimize the completion and stimulation design. This engineering workflow will enable to design and customize a particulate diverter system for effective fluid diversion and wellbore coverage by uniformly distributing the stimulation fluid with an aim to create fracture network complexities, enhancing the production. Additionally, this paper showcases the learnings from various field case histories including but not limited to drilling across weak bedding plane from Asia, wellbore stability issues in Middle East that resulted in high non-productive time from drilling, Uniform Fracture Growth from Horizontal Wells and re-fracturing strategies from North and South America. This approach will enable optimizing well performance from drilling to production, minimize risks and optimize intervention by retro alimenting each phase of the process to the next. This workflow provides a innovative strategic approach optimizing drilling, completion and stimulation mitigating challenges in unconventional formations that can be extrapolated to conventional reservoirs as well.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.