Developing a Field Strategy to Eliminate Crossflow Along a Horizontal Well

Abstract

Abstract This paper presents the results of a production log which revealed for the first time in Husky's experience with horizontal wells in the Rainbow Area, the existence of crossflows along an openhole horizontal wellbore. The production log indicated that the occurrence of crossflows along the wellbore reduced the effective producing well length to less than 25% of the total length. The thrust of this paper describes how a sound understanding of pool geology and reservoir heterogeneity, adequately transcribed to a numerical simulation model, is required to investigate and account for the crossflow phenomena. A horizontal well simulation model was constructed to test a number of hypotheses on how the crossflow was created. Through the very process of re-creating (history matching) the observed crossflow behaviour with the model, a comprehension of the most likely factors causing the crossflow was derived. A number of sensitivity runs were then made with the crossflow-matched model to determine ways of countering the crossflow. Based on the model predicted results, a field strategy was ultimately developed with the potential to eliminate the crossflow and restore the horizontal well to its true capability. Introduction The Rainbow Keg River "A" Pool is one of the seven mature hydrocarbon vertical miscible floods operated by Husky Oil Operations Ltd. in the Rainbow Field as shown in Figure 1. These mature floods are typified by a thin oil sandwich overlain by solvent/gas and underlain by water. Under such adverse exploitation conditions, Husky has successfully redeveloped these reservoirs through an aggressive program of horizontal drilling with the objectives of minimizing gas coning and/or channeling, increasing oil productivity and drainage area, and maximizing oil sandwich recovery(1–3). The technical aspects of drilling the first horizontal well into the "A" Pool have been described in Reference (4). Even though the eleven horizontal wells drilled to date by Husky have significantly improved pool productivities and economics, there is no definable correlation of well productivity to total openhole length. One of the technical challenges in horizontal well application is to understand the factors which cause non-uniform inflow along a horizontal wellbore, and where possible, eliminating those deterrents to the ideal of uniform inflow. More uniform inflow means that drawdown will be better distributed over the horizontal wellbore, leading to improved oil productivity, drainage and mitigation of local coning tendencies. FIGURE 1: Rainbow location map. Illustrations available In full paper. FIGURE 2: Rainbow Keg River,"A" Pool, geological facies/porosity map. Illustrations available In full paper. Production logging conducted by Husky on three of its horizontal wells has all shown uneven flow contribution along the horizontal length with intervals of no-flow contribution. In two instances, exemplified by production logs on the Rainbow Keg River "G"(2, 3) and "HP Pool(3) horizontal wells, lack of inflow appears to be the result of formation damage or poor reservoir quality(5, 6).