Building Three-Dimensional Structural Frameworks with Well-Log Data

Ross, William C.¹, Richard J. Langenwalter¹ (1) GeoGraphix, Highlands Ranch, CO

Structural frameworks are utilized by geologists as the basis for creating exploration and development drilling programs. A structural framework consists of a series of sub-parallel (i.e., non-intersecting) structural surfaces cut by one or more faults. Most framework building technologies utilize densely sampled seismic horizon data to constrain horizon and fault geometries. This study is focused on the specific techniques required to build frameworks from sparse well-top data. Building structural frameworks utilizing well-top data involves: 1) fault system modeling and networking; 2) structural surface modeling; and 3) integration of structure surfaces with fault plane and vertical separation information.

Three-dimensional surface modeling tools provide streamlined workflows for projecting and trimming hierarchical fault systems into a three-dimensional fault network. Once a fault network is in place structure horizon data can be projected into the faults and trimmed appropriately. Constraining the geometry of downthrown structure surfaces using sparse well-top data only, is a well-known subsurface problem. The problem is based on the limited number of wells that penetrate the target horizon on the hanging wall side of fault-related prospects. This study describes techniques for the progressive ‘down-building' of structural horizons using interval isochore maps to uniformly populate estimates of deep structural horizons. These structural surface estimates are then projected into fault planes and then adjusted to reflect the proper about of offset consistent with the locally mapped value of vertical separation.

By leveraging information from well-sampled shallow horizons along with vertical separation data from fault cuts, downthrown structural models are significantly improved. Results from model and real world test cases will be presented.