Stratigraphy

Talking Point:

(modified from Armentrout, 2000)

Stratigraphy is the study of the sequence, distribution, and nature of rock strata. Stratigraphic applications in the petroleum industry focus on characterizing the distribution and petrophysical parameters of hydrocarbon reservoirs, the seals that form traps for oil and gas deposits, and the source rocks that form petroleum.

The science of stratigraphy changed dramatically over the last 20 years, as compilation of data from sources as disparate as ice cores and regional seismic lines showed global changes in sedimentation patterns related to periodic changes in sea level. Nearshore systems such as rivers, deltas, and barrier islands are related to deepwater deposits of the continental slope and deep oceanic basins.

These systems are observed in nature and modeled through time with computer technology. Core, log and seismic data are used to calibrate and refine predictive models.

Carbonate deposits such as limestones present special problems in relating modern environments to ancient deposits. These may form in situ by biologic agents such as coral reefs. The distribution and characteristics of carbonate platforms evolved through geologic time with changes in environment and carbonate secreting biota. Many of these organisms are now extinct, so concepts for reservoir prediction and characterization in carbonates must combine knowledge of modern systems with age-based analogues.

Knowledge of geologic structures is also important to petroleum geology

Stratigraphy is the study of the sequence, nature and distribution of rock units.

Stratigraphic applications in the petroleum industry include definition of porous and permeable units that serve as hydrocarbon reservoirs, those impermeable units that seal the traps, and organic-rich strata that source oil and gas accumulations. Many stratigraphic studies focus on characterizing the distribution and petrophysical parameters for

• reservoirs in existing fields, and
• predicting reservoir presence and quality for exploration prospects.

For Clastic systems, sandstones and conglomerates plus new plays for low permeability reservoirs in siltstone and even shale

Sequence Stratigraphy and both deep water and deltaic depositional settings must be understood in relationship to each other, not in isolation.

Forward modeling and rock physics modeling help reduce the risk of unknown alternatives and improve interpretation understanding.

Core, log and seismic data to refine existing predictive models. Also, compiling reservoir parameters for debris flows versus turbidities utilizing flume experiments.

Carbonates present special problems in relating modern environments to ancient deposits. Carbonates may form in situ, not linked by not linked by sediment dispersal systems such as rivers, deltas, and submarine fans. In addition, the distribution and characteristics of carbonate platforms have changed through geologic time.

Concepts for reservoir prediction and characterization in carbonates must combine knowledge of modern systems with age-based analogues

Time-specific spatial maps of carbonate reservoir distribution are important as interpretation aids.

Along with Sedimentary Modeling Incorporating both clastic and carbonate processes and geometries.

Forward modeling, using computer programs to simulate depositional processes constrained by local characteristics of the sedimentary basin, can be important to understanding both carbonate and clastic systems