Modeling of Simultaneous Proppant Fracture Treatments in the Fruitland Coal and Pictured Cliffs Formations in the San Juan Basin

Abstract

Limited entry design techniques have proven successful for the simultaneous fracture stimulation of the Fruitland Coal and the Pictured Cliffs sandstone in the T28N-R7W Federal Unit of the San Juan basin, Rio Arriba County, New Mexico1. Optimization of this completion technique is dependent upon determining and placing the required effective propped fracture length in the coal and sandstone formations. This manuscript addresses utilizing limited entry techniques and a 3D fracture model. The model is then used to design N2 foam proppant fracture treatments in the coal and sandstone formations. This completion methodology allows reserves to be recovered from the Fruitland Coal at a significant cost reduction. With the different mechanical and reservoir properties of the two formation types, created fracture geometry will vary in each formation. Methods used to model these varied fracture geometries are discussed. Net pressure and production data analysis provide estimates for the effective propped fracture lengths in each formation. Radioactive tracer and production logs are presented as supporting evidence to validate the well completion design, the fracture modeling inputs and the stimulation of both formations simultaneously. Using this fracture modeling technology leads to increased reserve recovery and cost effective proppant fracture treatments. Introduction Typical hydraulic fracture stimulation methodology used by ConocoPhillips in the Fruitland Coal (FC) and Pictured Cliffs (PC) in the T28N - R7W Federal Unit consisted of two separate water based polymer nitrified fracture stimulations. The executions of these jobs were successful, but there was evidence in multiple wells that the created fracture had likely "grown"2 into the overlaying FC. Attempts to isolate the two formations proved both expensive and typically ineffective. With no zonal isolation, the gas reserves in the FC were not optimally recovered. Further, in wells where the created fracture in the FC was expected to remain contained, it was quite common to "break through"2 to the PC below, resulting in poor fracture connectivity in the coal. Proper application of limited entry design techniques has provided ConocoPhillips an opportunity to access previously unstimulated reserves at a significant cost savings by simultaneously fracturing the FC and PC formations. However, optimization of this completion technique is dependent upon determining and placing the required effective propped fracture length in the FC and PC formations. Ely, Holditch and Carter3 state that when the FC and PC have equal access to the fracturing fluid that it is difficult to determine resulting fracture propagation. Given the significantly different mechanical and reservoir properties of the two formations, the resulting created fracture geometry will vary unless a proper limited entry methodology is used. This work is a response to answer the questions of how to place varied slurry volumes in each formation and how to determine the effective fracture lengths in a limited entry or multilayer fracturing scenario. Geology The San Juan basin of northwest New Mexico and southeast Colorado has reported cumulative production of more than 17 TCF from over 30,000 wells producing from six main reservoirs4. In general for the T28N - R7W Federal Unit, the Pictured Cliffs Formation is a coastal barrier sandstone reservoir while the Fruitland Formation represents a related coal bearing fluvial system deposited behind the regression of the PC shoreline during the Late Cretaceous. Type III Fruitland Formation Coal, which is under pressure and requires no-dewatering for production, typically has a CO2 content less than 1% and a gas recovery factor of approximately 50%4–5.