Dula, William F.¹, Eddie McAllister¹
(1) Shell Exploration & Production Technology Research, 2280 AB Rijswijk, Netherlands

ABSTRACT: Basin Modeling Approach to the Prediction of Fault Rock Properties in High Net-to-Gross Reservoirs

Prediction of fault rock properties is critical where exploration prospects involve reservoir-reservoir juxtapositions and during field production when faults may baffle, or enhance (dynamic response), the flow of hydrocarbons. A forward modeling approach is described for predicting the paleo- and present-day properties of fault rocks formed at different depths and times in clean sandstones.
Given a description of the original clastic sediment (grain size, quartz and clay content, depositional porosity) and the burial/thermal history, the porosity and permeability evolution of the reservoir rock can be determined. The state of the reservoir (porosity, temperature, stress, and fluid pressure) at the time of faulting provide quantitative constraints on the texture and properties of the resultant fault rock which may then be modified by subsequent diagenesis. The tendency toward dilatency versus shear compaction is constrained by deformation experiments on high-porosity sandstones and unconsolidated sands. Fault rock grain size is also constrained by experimental data and is related to the effective pressure and the reservoir rock porosity and grain size at the time of faulting. Quartz cementation of the fault rock is tracked along with the undeformed reservoir sandstone. Permeabilities of the fault and reservoir rocks are estimated through various theoretical and empirical relations (e.g., modified Kozeney-Carmen), and the permeability contrast (k fault / k reservoir) is calculated throughout the remainder of the burial history.
The approach is illustrated using well, burial/thermal history, and core data from the offshore Netherlands. Implications of the timing of faulting, timing of hydrocarbon charge, and hydrocarbon retention are discussed.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.