Multilateral Waterflood Development of a Low-Permeability Carbonate Reservoir

摘要

The Shuaiba limestone reservoir of the Saih Rawl fieldrn(Oman) is a nearly unfaulted, low-relief structure of large arealrnextent. Permeability is matrix-dominated and relatively low (1rnto 10 mD). The reservoir contains approximately 90 10 6 m 3 ofrnlight oil (35 API) in column heights of typically 15 to 30 m.rnEconomical production only started in the early 1990's, 20rnyears after field discovery, when horizontal well technologyrncould be effectively introduced. Today, multi-lateral wells ofrnup to 7 legs are used in a pattern water-flood development.rnTotal open-hole lengths drilled in the reservoir have reachedrn11 km for a single well. To date, 166 km of producing and 107rnkm of injecting open-hole have been drilled, representing 167rnhorizontal legs, and yielding an oil production level of up torn9,000 m 3 /d (60,000 bbl/d). The original producer to injectorrnleg spacing of 250 m has gradually been decreased to 60 mrnand still fits the economic criteria.rnIn 2000-2001, a field development review was carried outrnto identify further development opportunities, both for thernshort and long term. A series of new reservoir managementrntools were put in place to predict the response of the reservoirrnto various development options. A pilot area was defined inrnorder to test these concepts and perform extensive datarngathering. Finally, new lab and feasibility studies wererninitiated. As a result from this review, a portfolio of short andrnmedium term activities was identified, including infill drillingrnto 40 m spacing, and drilling additional injection legs inrnexisting injectors. Also, upsides for developing the flank areasrnof the field (sub-15 m oil columns) were identified. Later,rnfishbone legs drilling and reversing water injection intornexisting producers will be piloted, while sweep optimizationrnmethods such as water shut-off and re-stimulation arernenvisaged to target recovery factors in excess of 50%.