Complex multiscale reservoir heterogeneity in a tidal depositional environment, Temblor Formation, West Coalinga field, California

Abstract

The Temblor Formation reservoirs in the densely drilled West Coalinga field were primarily deposited in various tidal settings and have an abundance of reservoir complexity types and heterogeneities that can be interpreted within a sequence stratigraphic framework. Characterization of the Temblor reservoirs is presented in three parts: the first part focuses on techniques of recognizing functional rock types using available logs, the second part focuses on interpreting depositional facies and stacking patterns in a sequence stratigraphic framework using available core, and the third part investigates two complex cases of reservoir continuity. As described in part I, the task of characterizing lithologies in the reservoir is a challenge because only the resistivity and porosity logs provide consistently useable information, and even then, with a number of caveats.As described in parts II and III, incised valley fills, associated with lowstand systems tract deposition above sequence boundaries, represent the dimensionally largest stratigraphic heterogeneities, are excellent completion targets, and can be imaged in three-dimensional seismic data as well as recognized in well sections. Incised valley fills typically consist of multistory tidal channel complex deposits. Mudstone intervals, locally diatomaceous, represent transgressive systems tract (TST) deposits and form vertical compartments in the reservoir. Highstand systems tract (HST) deposits include tidal bar and tidal channel deposits. Odd wedge-shaped bodies at a scale similar to that of incised valleys are also present in the upper Temblor reservoirs and represent deposition by backstepping (TST) and prograding (HST) systems tracts.At the bedset scale, thin mudstone beds, mudstone drapes, and mudstone clast conglomerates represent finer scales of heterogeneity. Localized carbonate-cemented zones can be mapped and represent important diagenetic heterogeneities that locally reduce net pay at the facies level. These well-documented different heterogeneity types can be used to address potential concerns in other tidal reservoirs being considered for development or in the early stages of production.