American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
Frequently, it is asked: "What is the best stimulation method for the San Andres formation? Under what conditions is it better to fracture, acidize or to fracture-acidize?" An objective of this study is to help in the designing of future treatments and evaluating previous treatments in similar type reservoirs.
This case history study is an evaluation of hydraulic fracturing, acidizing and fracture-acidizing treatments in approximately 25 wells in 5 fields producing from the San Andres formation in producing from the San Andres formation in the Permian Basin (Fig. 1). Most of these fields are now being waterflooded. Actual and theoretical productivity index ratios calculated by three methods were compared by plotting these ratios versus both actual and dimensionless times. Oil, water and total production rates were cross-plotted versus time production rates were cross-plotted versus time to help explain deviations of actual from the theoretical productivity index ratio curves.
A lithogical study has indicate that three basic San Andres rock types, lagoon, backreef and reef, resulted from variations in the depositional environment during the Permian Period of the Paleozoic Era. When the seas covered the Paleozoic Era. When the seas covered the present Permian Basin area, the larger present Permian Basin area, the larger particles of corals and fossil fragments particles of corals and fossil fragments settled and formed reef-banks in the high energy zone away from the shoreline. These reef-banks later formed high porosity, high permeability formations porosity, high permeability formations classified as reef type rock. Shelfward from these banks, the quiet water envirollment allowed finer particles to deposit which later resulted in the lower porosity backreef type rock. In the porosity backreef type rock. In the shallow water near the shoreline, even finer grained sedimentation eventually caused the formation of lagoon type rock. The lagoon type rock, at the present time, due to its low porosity, is generally not considered commercially productive of hydrocarbons unless it contains productive of hydrocarbons unless it contains natural fractures.