Modeling of horizontal well performance in bottom-water reservoirs with flow barrier.

摘要

Billions of barrels of light and heavy oil reserves remain trapped in the bottom-water reservoirs. A major problem for developing these reservoirs is that water coning during oil production results in decrease of oil production and increase of water production. In this thesis study, a new method is developed to improve oil production and reduce water production in the bottom-water reservoir by using flow barriers, which are defined as formation regions with low permeabilities underneath the horizontal well trajectory. More specifically, firstly, the effects of flow barriers on the horizontal well performance in the conventional bottom-water reservoir are evaluated by using three-dimensional numerical simulations. The effects of barrier permeability, length, width, and horizontal and vertical positions are comprehensively analyzed when a horizontal well is implemented as a producer. Secondly, combined applications of flow barriers and several oil recovery techniques, i.e., hydraulically fractured horizontal well, small-scale CO2 injection, and gel system injection, are qualitatively simulated to develop heavy oil reservoirs with bottom water. Thirdly, a novel three-dimensional reservoir-scale semi-analytical model is developed to model the horizontal well performance in a heterogeneous reservoir by computing the transient pressure responses and flow characteristics. In this semi-analytical model, the heterogeneous reservoir is subdivided into a number of homogeneous reservoir units and the horizontal well is subdivided into a number of segments. The reservoir unit and well segment are coupled at the interfaces of hydraulic contact. The method of sources and sinks is used to compute the transient pressure in the Laplace domain and the results are inverted numerically by using the Stehfest algorithm. The numerical simulation results show that the presence of the low-permeability barrier underneath the horizontal well delays water breakthrough and reduces water cut. Thus, a higher cumulative oil production and a lower cumulative water production are achieved. It is also found that a slightly permeable barrier is easier to convey the natural driving energy of bottom water than a sealing barrier and that a larger size barrier ensures higher oil recovery. In addition, the detrimental effect of the bottom-water coning can be further alleviated in heavy oil reservoirs by applying the above-mentioned combined applications. On the other hand, the newly proposed semi-analytical model enables the reservoir heterogeneities, e.g., low-permeability regions, to be detected by transient behaviors. The semi-analytical model can also be applied to study the transient behavior of heterogeneous reservoirs with the areal and vertical extent. Furthermore, the three-dimensional display of the flow flux distribution within the reservoir provides a better understanding of the reservoir heterogeneity and connectivity.