Stimulation Of Horizontal Wells Using Diverted Acid Treatments

Abstract Quality stimulation of a horizontal well is often difficult to achieve due to economic or physical constraints. In Southeastern Saskatchewan, many horizontal wells are being drilled and completed with new technology which is now being developed. This paper describes the development of stimulation technology that is economically attractive and operationally feasible for some horizontal well operators. Two case studies are presented that show technological development and implementation. Reservoir properties, drilling methods and wellbore configurations were examined to determine possible stimulation techniques. Stimulation options examined were: acid washes, selective acid or solvent squeezes and diverted acid treatments. Diverted acid treatments were chosen as the most economical stimulation. The balance of this paper describes the methodology including research, quality control and execution of the operation. This paper concludes with a post stimulation evaluation that highlights the favorable economics of thorough research, quality control and design practices. Introduction Many of the horizontal wells drilled in Southeastern Saskatchewan have required some type of stimulation to improve production. In Southeastern Saskatchewan, Figure 1, the need for performing a stimulation on a well is generally due to either a declining fluid production rate, or a declining oil production rate. In some cases, an increasing watercut may require work of another type prior to carrying out stimulations. Such treatments include packers to isolate the high water producing intervals from the producing wellbore. Two wells were stimulated in the Ingolds by field of Southeastern Saskatchewan last Fall. The wells were completed with an open hole horizontal section in the Frobisher formation. The Frobisher formation, contoured in Figure 2, is composed of dolomitic limestone with natural fractures. The fractures may be open or infilled with natural occurring reservoir rock constituents. A strong water drive from the underlying Alida formation is predominant in the area. The first horizontal well stimulated in this pool, Tai A11-13, had been placed on production without any stimulation following drilling with a KCI polymer mud in October, 1991. Due to a rapid decline in production, mud filtrate and drilled solids damage were suspected. The second horizontal well stimulated in this pool, Tai 10–12, had been placed on production without any stimulation following drilling with a KCI polymer mud in October, 1990. With the decline in fluid production, a stimulation was warranted and performed simultaneously with other work on the well. Following a review of the well files, extensive research and lab testing was performed in an attempt to determine the optimal stimulation technique, prior to performing each of the diverted acid treatments. A 15% HCI acid system with gelled water diverter was used in both wells. In the second stimulation, the 15% HCI acid system also included 30% Xylene by volume. Execution process Both of the wells followed a similar execution process. The execution of each stimulation began with a thorough well review. Prior stimulation of offset vertical wells in the immediate surrounding area were reviewed. Treatments to offset horizontal wells were investigated for the type of stimulation, the field execution, and prior and post production data