A New Diagnostic Method for Prediction of Producibility and Reserves of Wells Producing From the Monterey Formation Using Well-Log Data

Abstract

Summary Formation evaluation with well-log data is primarily a prediction tool for the purpose of identifying porous and permeable zones containing movable hydrocarbons. When the lithology is complex or the productivity is controlled by fracture density and the welllog data are limited in scope, underestimation of productive intervals can occur. This paper is a unique study on relating more than 28 years of actual production history to the initial well-log responses. This retrospective approach is the basis for presenting a diagnostic approach to predict producibility and reserves for other wells in the field under study or in other neighboring fields with similar geology. The focus of the study is well-log responses in the Monterey formation, offshore California. The geology of this formation is regarded as a prime example of a heterogeneous matrix system and a lithology-dependent fracture network. The lithology of the Monterey formation is heavily influenced by the diagenetic stage of biogenic silica (comprising the bulk of the geologic column), the detrital content, and the calcareous component. The particular field selected represents the typical lithological and diagenetic stages observed in surrounding fields. As such, the proposed approach has merits for application to other fields. Geographically, the Monterey type sediments extend from Baja California all the way along the Pacific Rim to Japan.1 Extension of the lithological patterns observed and the productivity correlations in surrounding fields can lead to eventual development of a more general correlation for widespread exploratory or development wells in this type of formation.