Depositional sequences and integrated recovery efficiency forecast models for San Andres and Clearfork Units in the Central Basin Platform and the Northern Shelf, west Texas

Abstract

This paper develops depositional sequences of the carbonate ramp and the carbonate shelf models for an idealized cycle and multiple cycles of depositions. Based on the developed depositional sequences, the integrated recovery efficiency forecast models of primary, initial waterflood and infill drilling are developed for the San Andres and Clearfork reservoirs in Central Basin Platform and the Northern Shelf, west Texas. The geological parameters and well spacing are considered major factors for controlling recovery efficiencies. The depositional environment and diagenesis are controlling geological factors affecting oil recovery efficiencies. The depositional sequences characterize the vertical and lateral variations of depositional-energy environments in development of the carbonate ramp and the carbonate shelf The depositional-energy environment controls the depositional rock's facies. The well-sorted and large-size grainstones are related to the higher depositional-energy environment. The poorly-sorted and small-size rocks are related to the lower depositional-energy environment. The depositions of the San Andres and Clearfork formation in the Central Basin Platform, separately, follow the prograding-ramp sequences of one major cycle with multiple subcycles. The lumping depositional energy increases from the inner platform to the platform boundary. Similarly, the depositions of San Andres and Clearfork formation in the Northern Shelf also follow one major prograding cycle with multiple subcycles, separately. However, the lumping depositional energy, decreases from the inner platform to the platform boundary. A normalized depositional energy index is defined based on the depositional sequences of the ramp and shelf models. Normalization is also used to define a porosity index and a well spacing index. Linear and exponential regressions on a database are conducted to develop recovery efficiency forecast models which include depositional energy, porosity and well spacing indices. Section 17, Dollarhide Clearfork Unit is used as an example to show the applications of the recovery efficiency forecast models.