Frac Hit is an inter-well communication event where an offset well is affected by the pumping of a hydraulic fracturing treatment in a new well. Close well spacing, increased fracture density (number of fracs per well), and larger fracture treatments increase the chance of a Frac Hit. This paper demonstrates how a Geographic Information System (GIS) was used in the Barmer Hill oil reservoir to quantify the risks of a Frac Hit on a well by well basis.
The Aishwarya Barmer Hill (ABH) field (<1 mD/cp) overlies the prolific Aishwarya Fatehgarh (AF) field (>3 Darcy's). The AF field was developed first with 71 wells. All of these wells for AF reservoir penetrated through shallower ABH reservoir at an average spacing of ∼100 m. The ABH field development plan calls for 1000 m long horizontal laterals with a ∼180 m distance between the wells to efficiently drain the entire ABH structure. The hydraulic fractures planned in ABH wells had an average fracture half-length of ∼100 m with 10 stages per well. With the spacing equal to the fracture half length, the likelihood of a Frac Hit between ABH horizontal wells was high. The presence of the nearby AF wells only added to the risk.
GIS enabled software was used to evaluate the risk magnitude and the observations were used to prepare a mitigation plan. All the well trajectories for both reservoirs were mapped inside the 3D reservoir structure. As a first case, a potential strike zone (PSZ) with a radius equal to the frac half-length was generated around the planned ABH wells. Wells were considered at risk if a PSZ intersected another well or another PSZ. Then all of the planned hydraulic fractures were mapped in 3 dimensions using the known fracture propagation azimuth (from appraisal well micro-seismic data) and the simulated fracture dimensions (Half-lengths & heights) using fully 3D frac modeling software.
The procedure clearly identified the cases (well/stage) which had a high potential for a Frac Hit. After identifying the high-risk cases, appropriate steps were taken to minimize the risk. The available options were to change the well trajectory, modify the fracture location (shift or remove stages), or propose additional surveillance.
The Frac Hit phenomena is a sub-surface integrity related concern which has been reported on in many technical papers. This work proposes a method for quantifying and minimizing the risks using a GIS platform. A method for categorizing the various risk cases based on well spacing, perforation and fracture initiation points is proposed. This method was studied for the ABH wells during the well planning phase and shall be applied in order to minimize Frac Hit risks. The information provided could also be directly utilized for in-fill development project for tight fields.