Abstract
An integration of surface and subsurface models for a deep Gas Condensate field in Oman, containing condensate rich gas in reservoir A (shallower) and dry gas in reservoir B (deeper) is the content of this paper. Production to date was mostly from reservoir A, at which all wells are completed, resulting in the reservoir pressure dropping by 60% in some specific locations from the initial pressure. Furthermore the layered nature of the reservoirs and the varying hydraulic fracturing of the different units, production from the various units differed significantly resulting in significant vertical differential depletion of the reservoir. The field's CGR (Condensate Gas Ratio) has dropped by more than 50% as a consequence of liquid drop out resulting the reservoir A pressure dropping to below the dew point pressure, and the increasing dry gas production from reservoir B through commingled production from some of the wells.
The main challenges in the field is predicting the well performance which is affected by the flow impairment caused by the condensate dropout, the quality of the placed hydraulic fractures in terms of their efficiency and geometry, and completion type, single reservoir or commingled in the two reservoirs (A & B). Also, sealing and non sealing nature of faults play a big role in well performance in the long term. This makes predicting well performance a very complex undertaking.
Integrating Surface and Subsurface models of gas/condensate wells in tight reservoirs with liquid drop-out is still one of the most challenging subjects in reservoir engineering today, especially when it is used as a tool for improving operating philosophy. This integrated project provides an overview of actual reservoir performance in the field over the first 6 years of its production life and the impacts of surface/subsurface integration. For example, high well declines have been observed (upto 50% per annum), the effect of fluid mixture of the rich and dry gas, resulting from the commingled production, the potential cross-flow of the dry gas to the rich gas as was indicated by condensate production and the well capacity, Compression size and timing and operating philosophy. Dynamic models, calibrated by historic production data, are used to assess these effects and to predict future production performance.
