Competent Utilization of Multistage Acid Fracturing Technology to Increment Well Productivity during Stimulation of Low Permeability Gas Carbonate Reservoirs – Case Study

Abstract

Tight gas reservoirs and specifically low permeability gas-bearing carbonate formations require stimulation to produce commercial gas rates. Certain carbonate reservoirs in Saudi Arabia are highly heterogeneous and the degree of heterogeneity changes over the field and within well drainage areas. Horizontal multi-stage acid fracturing technology has become the preferred completion method in such reservoirs to stimulate these carbonate formations to maximize reservoir contact and enhance well productivity. Due to the degree of heterogeneity of these formations, a number of factors should be considered and a set of best practices should be implemented to overcome the reservoir challenges and achieve the expected results. Maximizing stimulated reservoir volume is one of the key aspects of the success of this technology. To maximize the stimulated reservoir volume, effective placement of the hydraulic fractures for every stage must be achieved, which is one of the most challenging factors. Effective placement of hydraulic fractures depends mainly on the following factors: placement of the horizontal wellbore along the minimum-stress direction and proper annular isolation to induce independent fractures across each stage. This goal becomes even more challenging to achieve with acid fracturing treatments. Failure to isolate the stages can lead to hydraulic communication between the fracture stages, allowing the pumped frac stage to propagate to the previously open frac stage, preventing the creation of separate fractures, affecting the well's productivity and ultimate recovery. A second factor that governs multi-stage completion effectiveness is the use of swellable packers to ensure proper isolation between the various stages, which was observed in the field. This paper describes the application of Multi-Stage Fracturing (MSF) completion technology. Field cases describing the deployment of the MSF completions and the obtained results after stimulation is presented, as well as the main conclusions and recommendations for successful implementation of this technology are highlighted.

Analysis of Flow Behavior for Acid Fracturing Wells in Fractured-Vuggy Carbonate Reservoirs

“…Therefore, wormholes, together with artificial fractures, form the main channels of the fluid flowing into the wellbore. At present, acid fracturing has been widely implemented to enhance productivity of wells with damaged zones or produce from tight carbonate reservoirs [23][24][25]. Unfortunately, complex seepage systems created by this stimulation pose challenges to study the transport processes in underground natural-resources recovery.…”