Paper: Completion Stimulation Programs In The Spraberry Trend of West Texas

Increased demand for crude oil and the higher prices being paid for petroleum products have caused a resurgence of activity in the Spraberry Trend of West Texas, (Fig. 1). Even though it is one of the largest producing areas in the industry it has always been somewhat of an enigma to those working with it. However, with proper planning and execution of the completion phase, new wells in the Spraberry-Dean sections, and re-. completions in the Dean zone can be economically attractive. The Spraberry and Dean zones are primarily siltstones with very low matrix permeability and porosity. Extensive natural fractures occur throughout the zones. It is the existence of these fractures that provides enough fluid movement and fluid storage to make completion from the zones economically feasible. Due to the nature of these formations, they require a successful hydraulic fracture treatment to provide the needed productivity. Two very influential factors to be considered in planning the stimulation treatment are: zone separation and fluid selection. In order to properly stimulate each zone, it is necessary to keep them separate during the stimulation process. The existence of natural fractures favors extension of the induced fractures beyond the vertical limits of the perforated intervals. In addition, there is a significant difference in the fracturing pressures of the zones, thereby creating a pressure differential across any unperforated interval. It is general practice to maximize the length of this unperforated zone of separation. One popular method for staging the subsequent stimulation treatment is the "ring and bomb" procedure; another is to take advantage of this natural pressure difference between the Dean and Lower Spraberry zones to effect sequential stimulation without benefit of mechanical separation. When stimulating formations with low permeabilities it is necessary to create deeply penetrating fractures in order to obtain adequate drainage. In the case of the specific formations under consideration, large induced fracture heights occur regularly. The end result is the creation of very large fracture areas requiring large quantities of frac fluids. Therefore, it is very important that the fluid chosen provides a balance of fluid efficiency, cost, characteristics. and clean-up Production data on a well-to-well basis is erratic; however, studies of selected groups of wells lead to the general conclusion that bigger frac jobs provide for more ultimate oil recovery. This return on investment is an exponential function and experimentation is still being conducted in an attempt to better define the optimum limits. In addition to fracture penetration, the sand program used and the fracture widths created seem to also have an effect on the production history.