Multi-stage acid fracturing in a tight carbonate formation can be an alternative to propped fracturing as a relatively cost-effective completion treatment. However the success of the treatment depends on many factors as to whether enough conductivity by acid etching has been created, and weather the selected chemical treatment has worked well in-situ under the specific geologic environment. Thus, observation and evaluation of past practice is important to develop further optimal stimulation procedures. In this paper, an integrated methodology to conduct performance evaluation of multi-stage acid fracturing treatment in a horizontal well is presented. The method is applied to a field case in Tarim Basin in China.
The integrated procedure starts with obtaining closure pressure and the formation breakdown pressure. Bottomhole treating pressure is then estimated from surface treating pressure in cases if it is not measured directly. A treatment pressure history match is then conducted to estimate the fracture geometry using commercial software. A 3-D acid fracture conductivity profile is generated using the in-house acid fracture simulator. Then using the reservoir face pressure and the acid fracture conductivity profile obtained by the acid fracture simulator, the cross-sectional flowing area created by acid fracturing fluid is estimated using pressure transient analysis. Evolution of fracture extension and acid etching during the stimulation is calculated assuming a bilinear flow regime. After production starts, a linear flow diagnostic approach provides the cross-sectional area flowing that has the flow from the matrix. This enables us to compare flowing cross-sectional area with induced area by the stimulation, which is defined as treatment efficiency.
A field application based on the proposed procedure shows the effectiveness of the approach. The integrated approach provides engineers with additional information as to whether the designed acid fracturing has been performed appropriately under high closure stress field. It is eventually helpful to discuss past practice and improve candidate selectivity in a company decision making process.