Well test problems of Cenomanian reservoir with the presence of a permeable barrier

DOI: 10.24412/2076-6785-2023-8-70-74

Abstract
The article provides an analysis of well tests of horizontal wells producing in Cenomanian reservoir. A feature of the reservoir is the presence of a permeable shale barrier between two layers, initially accepted as a non-collector. However, as the field was developed, assumptions arose about the possibility of drainage of the entire gas-saturated thickness. This fact became the basis for revising the research results.
Some wells showed a drop of pressure build-up derivative. Previously, the derivative drop was assessed as a data distortion associated with smoothing algorithms for noisy data. Reviewing of the well test results showed the possibility of more complex reasons for this behavior such as active influence of the gas-water contact or the producing of the entire gas-saturated interval. To clarify these assumptions, there were performed numerical simulation.
Simulation results showed responses similar to producing of the entire gas-saturated thickness through a permeable shale barrier without the influence of the gas-water contact. The analysis results confirm the producing of the second layer through the barrier and enforce the restrictions to the well operating conditions in order to prevent premature watering due to a rise in the level of the gas-water contact. This allows to increase the final gas recovery factor by 5%.

Materials and methods
As initial data, the article considers the well test results of Cenomanian reservoir. During the work, build-up log-log graphs were analyzed and categorized depending on the type of responses and well construction. To confirm the assumptions made, a numerical simulation was performed for cases of a vertical and horizontal well with different values of the barrier permeability.

Keywords
well test analysis, pressure build-up, Cenomanian reservoir, layered reservoir, horizontal wells