Lessons Learned From Modeling Hydraulic Fracture Treatments in Coals Using a Fully Functional Three Dimensional Fracture Model in a San Juan Basin Project

Abstract

fax 01-972-952-9435. AbstractThe two main objectives of using a hydraulic fracture model in coals are: (a) optimization of job design and placement, and (b) post-fracture diagnostics. Though certain limitations still exist, hydraulic fracture modeling in coals has undergone major advancements in the past decade. Pseudo or lumped three-dimensional (3-D) models have usually been employed to try and meet the objectives mentioned above. The effectiveness of using such models in coals has been very limited. Fully functional 3-D models are currently available in the industry and can be used to obtain better estimates of the fracture dimensions. This paper shows that a grid-oriented fully functional 3-D fracture simulator with shear decoupling can be especially useful in coals for post-fracture diagnostics if sufficient input data can be fixed from logs and Diagnostic Fracture Injection Tests (DFIT).When problems occurred with placement of fracture treatments, especially in the upper Fruitland coals of a San Juan basin project, instead of experimenting with various ideas arbitrarily, technical evaluation using DFIT data and fracture modeling with a grid-oriented, fully functional 3-D fracture simulator, was used to pin-point the issues and address them accordingly. This paper will discuss the deficiencies of using 2-D and pseudo-3-D fracture models in coals and also will discuss the lessons learned from using a grid-oriented, fully functional 3-D fracture simulator in this project along with the successful implementation of the results developed from the modeling work. Literature ReviewOver the last 25 years, numerous papers have been published regarding hydraulic fracturing and modeling in coals. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] et al. 1 investigated how well the fractures are contained in coal during a stimulation treatment. In this study, 12 vertical wells were drilled, completed, and subsequently evaluated via mining excavation. The treatment designs were adjusted using the information gathered from excavation. Layne, et al. 2 through their U.S. Department of Energy (DOE) work wanted to advance the hydraulic fracturing techniques in coals by improving the understanding of fracturing treatments using mineback observations. They used five fracture models that were developed under contract to the DOE to analyze the mineback observations. Jones, et al. 3 evaluated 130 fracturing treatments in their study. They observed high treating pressures during fracture treatments in Black Warrior basin and attributed the following as possible causes: (a) high pore pressure buildup due to fluid leakoff, (b) multiple fracture propagation, and (c) fracture-tip plugging by coal fines. They modified a pseudo-3-D model to replicate a fracture tipscreenout caused by coalfines plugging within the pad. Jones, et al. 4 presented another paper addressing the unusual treating pressures observed during hydraulic fracture treatments in coal. As part of that work, they presented methodologies to design fractur...

Effects of High Pressure-Dependent Leakoff (PDL) and High Process-Zone Stress (PZS) on Stimulation Treatments and Production

“…The following summary from the examples provided by the author in earlier publications (Ramurthy et al, 2007 and) confirms it. This can be used as a grading tool to identify potential stimulation candidates.…”

“…In the coal example (Well-A) at a depth of 904-to-970 ft presented by the author (Ramurthy et al, 2007 and), the stimulation treatment was designed to pump 54,000 lbm of 16/30-mesh proppant with the low gel-loading hybrid fluid system at a rate of 35 bpm. However, the job screened out when the 2-ppg sand reached downhole with only 8,300 lbm of proppant placed.…”

“…Pressure-outs are more common with high PZS than screen-outs (Ramurthy et al, 2007). This assumes that all or majority of the perforations are open and there is minimal near-wellbore friction.…”

Evaluating Hydraulic Fracture Effectiveness in a Coal Seam Gas Reservoir from Surface Tiltmeter and Microseismic Monitoring

“…Once a robust in situ stress profile was constructed, several fluid and proppant volumes were evaluated using a planar, three-dimensional, grid-oriented, finite-difference hydraulic fracture modeling simulator (GOHFER) capable of modeling: the complexities of pressure-dependent leakoff; potential fluid losses to transverse or complex fracture geometries; and potential variabilities in tectonic or process stress environments around the target coal seams (Barree 1983, Conway and Barree 1998, Ramurthy and Lyons 2007. In the course of pre-fracture design process, it was decided to lump the fracture stimulation of the range of Upper and Lower Juandah and Taroom intervals across Ridgewood 5 and 6 into six stages between the two wells.…”

Effects of High Pressure Dependent Leakoff and High Process Zone Stress in Coal Stimulation Treatments

“…This was done to identify and eliminate the reasons for the observed high treating pressures prior to the restimulation treatment. The detailed explanation provided by Ramurthy et al 5 is the main reason for choosing this fracture model in this study. The history-match analysis of the fracture treatment is shown in Fig.…”