Characterization of high-permeability streak in mature waterflooding reservoirs using pressure transient analysis

• A mathematical model is established for waterflooding high-permeability streak.
• Pressure performance of high-permeability streak is analyzed.
• Gravitational Search Algorithm is applied to characterize high-permeability streak.
• This approach has been employed in many China Oilfields.
• Field cases are presented to substantiate its validity.

The characterization of thief zone, which evolves from long-term waterflooding, has become imperative in the enhanced oil recovery process. As one typical kind of thief zone, pressure transient performance of high-permeability streak is analyzed in this work. A mathematical model is established for a well intersected by a high-permeability streak, and the solution in Laplace space is derived by Ozkan's source function. To ensure improved accuracy and better efficiency, the solution is inverted into real space numerically through de Hoog Algorithm.Investigation of the pressure transient behavior indicates that the process can be divided into three periods: (1) the early-time flow period, which is comprised of streak storage-type flow and bilinear flow; however, it occurs too early to be of practical interest; (2) the linear flow from the formation to the streak, which is characterized by a half-slope straight line; (3) pseudo-radial flow, exhibited by a horizontal line on the derivative curve. The sensitivities of corresponding parameters have also been discussed.Furthermore, Gravitational Search Algorithm (GSA) is successfully applied as a non-linear regression technology to match measured pressure with this model and to characterize high-permeability streak. Compared to previous technologies, this approach is more cost-effective and less time-consuming. Moreover, the quantitative characterization of high-permeability streak can play a very important role in the design of conformance control project. Thus this approach has been extensively employed in many China Oilfields. And field cases are also presented to substantiate its validity.