RESERVOIR ENGINEERING

Designing of A Waterflood For Spraberry Trend

Designing of A Waterflood For Spraberry Trend

Spraberry Trend discoveries and field development plans of the past five years involve middle Miocene to Paleocene reservoirs with lower porosity and permeability resulting from compaction and cementation. In this setting, rock compaction may be less important as a production drive mechanism, and aquifer support (possibly augmented by water flooding) assumes more significance. Porosity and permeability decrease is related to greater burial depth and compaction as well as temperature-related cementation. Structural styles of these fields include compressional anticlines, turtle structures, and sub-salt three-way dip closures. Some of these structures are highly compartmentalized by faulting. (Dake 2009)

We used an experimental design approach to analyze dynamic simulation of two static models loosely based on the stratigraphy and reservoir properties from a thick-bedded reservoir and a thinner-bedded Paleocene. Modeled variables included geological parameters (structural dip, faulting, facies, and aquifer size), reservoir parameters (absolute permeability and heterogeneity), fluid properties and production variables. The results of the dynamic simulation were evaluated using Experimental Design. The interpretation process involved five steps: identifying uncertainty parameters and ranges, running simulations for a wide variety of parameters, generating relationships of recovery factor as a function of uncertainty, identifying parameter importance, and determining incremental oil recovery due to water injection. For these experiments, the incremental recovery for aquifer-supported fields is small with a P50 value of 7%. Key water-flooding variables are depofacies, aquifer size, permeability, fault transmissibility, and oil saturation. (Craft 2010) The least important are bed dip, injection voidage-replacement, and PVT properties.

Spraberry Trend discoveries of the past five years are in water depths greater than 4000 feet and in older Tertiary reservoirs of middle Miocene to Paleocene age. Structural styles of these lower slope fields include compressional anticlines, turtle structures and sub-salt three-way dip closures against salt faces (Figures 1 and 2). Some of these reservoirs are highly compartmentalized by faulting. In this setting, rock compaction may be less important as a production drive mechanism, and aquifer support (possibly augmented by water flooding) assumes more significance. Porosity and permeability decrease is related to greater burial depth and compaction as well as temperature-related cementation. (Dake 2009)

Much of the production experience in the Spraberry Trend is from upper Miocene through Pleistocene reservoirs. The characteristics observed in these reservoirs and fields are summarized as follows:

Pay often consists of stacked reservoirs.

Permeability, porosity, and oil properties are good, resulting in high ...