Abstract
An enormous quantity of geologic, engineering, and geophysical data exists in most U. S. petroliferous basins. The quantity of data can be overwhelming to personnel who routinely work under time and data-handling constraints. Techniques for building and managing a large database in the PC environment---the platform of choice by many smaller companies---can provide new exploration and development opportuities by maximizing use of these large data sets.
We have built a database of >1100 wells in a 70 section area which includes the oil- and gas-producing Terry Sandstone in the Hambert-Aristocrat Field, Denver Basin. Database construction consisted of a series of iterative information flows comprising four phases: (a) compilation (what is required to solve the problem?), (b) extraction (gathering, organizing, and storing data for quick and easy access), (c) interpretation (processing, describing, translating, comparing, combining, correlating, and calculating the data), and (d) analysis (interpretation and synthesis). Once constructed and analyzed, this large data set provided a more comprehensive and complex geologic reconstruction of the field area than previous studies, from which new opportunities were identified.
Specifically, the Terry Sandstone is both structurally and stratigraphically compartmentalized. Compartmentalization controls reservoir fluid distributions. A dominant northeast-trending fault system, with a secondary northwest trending system, compartmentalize the Terry Sandstone into numerous relatively small fault blocks (some < 0.5 miles across). Faults appear to be sealing, as evidenced by consistent patterns of: (a) higher normalized GOR's of structurally higher wells within a single fault block and/or of wells in upthrown blocks than of wells in downthrown blocks and (b) calcite-filled faults or fractures, as observed in core and on density logs.
Stratigraphically, the Terry Sandstone consists of a series of at least seven stacked shoreface parasequences within an overall transgressive systems tract. Best reservoir quality rock, and most production, occurs within upper shoreface strata immediately above a regional sequence boundary. Lower shoreface/offshore strata contain thinner, but relatively permeable sandstones which appear on well logs as possible low resistivity-low contrast intervals (potential 'missed pay'?). Transgressive shales which separate parasequences provide the potential for stratigraphic sealing and vertical compartmentalization. Directional or targeted infill drilling, for example, might provide additional reserves in this complex setting.
Since faults penetrate the entire Cretaceous section and shoreface strata are thought to be common in the Denver Basin, the results of our analysis of this large database can be more widely applied to this basin, as well as to perhaps other Rocky Mountain basins for improved exploration and field development projects. In this instance, construction and use of a large database has provided insights into the complex geology which would not have been achieved with a more restricted, or 'representative' data set.