Multistage Acid Fracture Effectiveness in Gas Production in the Carbonate Reservoir, Saudi Arabia - Study and Analysis of Field Examples

Abstract

For last few years, multistage acid fracture treatments have become a common practice to develop the carbonate gas reservoirs in Saudi Arabia. Different multistage completions systems have been used in more than 50 wells that were acid fractured anywhere from 2 to 6 stages per lateral. These systems include multistage fracturing (MSF) with openhole frac sleeves in combination with open hole hydraulic or swellable packers to provide zonal isolation between fracture stages. This paper provides an analysis of the effectiveness of these fracturing treatments comparing the pre-and post-frac gas production rates of the wells as functions of fracture half-length, conductivity, and some of the main reservoir properties such as porosity and flow capacity.One major concern from the open hole MSF treatments is the zonal isolation provided by the open hole packer assemblies. This is very important to ensure fracture containment for the zone the induced fracture is intended for. Failure in isolation can lead to communications between intervals allowing the pumped frac stage to propagate to the previously opened frac stage. This could result in fracturing less number of stages than designed. Consequently, the expected production rate may not be achieved. This study also analyzes the post-frac pressure build up response for selected carbonate reservoir wells to compute number of effective fractures created during the treatment. The reason of isolation failures and how to avoid that in the future MSF treatments are discussed in this paper. Several field data including post-frac production data have been analyzed for MSF acid fracturing in the carbonate gas reservoirs to establish the treatment effectiveness. This analysis will be useful to optimize the future well stimulation programs and improve gas production.