Abstract: Impact of Diagenetic Processes on Sandstone Reservoir Quality: Controls, Effects, and Predictive Evaluation Using Data from Natural and Experimental Systems

LARESE, RICHARD E.

Sandstone reservoir quality is significantly influenced by diagenetic processes that are often programmed by pre-burial conditions of tectonic setting, depositional facies, and framework composition. The integration of natural and hydrothermal
experimental rock-fluid data can be extremely useful in the predictive evaluation and modeling of porosity-modifying diagenetic processes within sandstone reservoirs at depth. Commonly, lithologic data may be limited or nonexistent in deeper reservoir intervals comprising frontier and even mature basin plays. In these instances, laboratory simulation of diagenetic processes permits the evaluation of porosity reduction, preservation, and enhancement mechanisms that may significantly impact exploration strategy and anticipated exploitation/production problems. Subtle variations in diagenetic lithification/alteration can appreciably affect reservoir compressiblity and well-bore stability characteristics during petroleum production.

Considerable emphasis has been placed on the evaluation of diagenetic processes controlling relative preservation of primary intergranular porosity on field-regional scales. These processes include argillaceous and siliceous grain coatings, hydrocarbon "poisoning," and overpressure. In several Mesozoic clastic intervals within the Gulf of Mexico and North Sea, optimum reservoir quality occurs in sandstones possessing approximately 5--13 vol. % chlorite coatings that are sourced in part by chemical alteration of in-situ labile lithic material. Moreover, experimental evidence suggests that liquid hydrocarbon can effectively retard quartz/clay cementation and compaction processes in sandstone reservoir intervals. Liquid petroleum appears to significantly retard pressure solution compactional effects under both oil-wet and water-wet conditions. Although liquid petroleum retards physical compaction effects in lithic-rich sandstones under oil-wet conditions, its effectiveness on "poisoning" of ductile deformation effects is greatly dependent on interactive chemical stability of framework grains and timing of emplacement. Correspondingly, simulation of "early" overpressure effects on physical compaction in lithic sandstones indicates a porosity increase of 1.3--2.8 pore units per 1000 psi (6.9 Mpa) overpressure, depending on the ratio of brittle to ductile framework components.

AAPG Search and Discovery Article #90938©1997-1998 AAPG Distinguished Lecturers