This paper addresses some key reservoir and production issues related to gas and condensate recovery from Khuff reservoirs in the Middle East – namely Ghawar Khuff, North Field and South Pars. These fields represent somewhere between 1,000 and 2,000 Tcf initial gas in place, with 30 to 70 billion barrels of condensate in place. We apply engineering methods and reservoir simulation to quantify the expected performance of Khuff gas condensate fields for a realistic range of geologic description, petrophysical and fluid properties, and production facilities based on published information.
We review key data for reservoir and production design, summarizing the impact of geologic zonation, areal and vertical communication, mean permeability and its variation, relative permeability, water encroachment, and fluid composition on field performance. Because most commercial development projects involving gas sales export are based on delivery contract quotas (DCQs) of 1–1.5 bcf/D for up to 25 years, well-average plateau length and rate-time is used as a primary measure of performance.
We try to describe the interplay of reservoir and production-facilities performance on overall design of field deliverability and total well requirements. Other production issues not considered in our work but with significant impact on Khuff development strategy include gathering system design, rate metering, platform vs. onshore processing, and single-phase vs two-phase pipeline flow. Economics are not considered in our evaluation.
We estimate deliverability impairment from condensate blockage using relative permeability models that reflect the impact of velocity (capillary number improvement and inertial effect). The velocity effect is particularly important in Khuff wells because of the high-k, low-h layers with unusually-high flow velocities and convergent flow.
Layer vertical and areal connectivity can have a profound effect on water encroachment. When sufficient lateral continuity exists, even small aquifers can result in rapid water encroachment through thin, high-permeability zones. This has been studied and is shown to have a lesser effect in Khuff reservoirs.