The Dynamic Pressure Response Of A Petroleum Reservoir: A Field Case Study
Authors: Shuck L. Zane , Komar Charles A. 
Published: December 2007

The results of a comprehensive 18-well, water-injectivity test series in a 41-well petroleum reservoir to delineate subsurface fracture systems and evaluate their influence on efficiency of an enhanced ail recovery process are explained in a documentary type film. The dynamic response of the reservoir to the short-term injection tests is described and interpreted. Significance of the results and their importance in designing well patterns for enhanced oil recovery projects are patterns for enhanced oil recovery projects are emphasized.

Six of the 18 different well tests with complete data sets are shown. These complex, time-dependent data are interpreted using animated computer graphics generated 3-D pressure plots. Comparisons of dynamic data generated from computer simulation models of pressure buildup in unfractured and hydraulically pressure buildup in unfractured and hydraulically fractured reservoirs with applications to oil recovery by waterflooding are also demonstrated.

Results of a 10-year waterflood project in the reservoir support the fracture system interpretation derived from the tests and the conclusion that linear displacement efficiency had been achieved from the aligned fractured-well pattern. Conclusions evolving from the documented field case study emphasize:that enhanced oil recovery projects should always be investigated in light of subsurface fracture systems and stress fields before any fluids are injected for oil displacements; and,that animated computer graphics analyses of pressure tests arc an effective means of delineating subsurface fracture systems and characterizing reservoirs.

Introduction

The real effects of producing fluids from the earth's crust or injecting fluids into it have perplexed engineers and scientists throughout the world perplexed engineers and scientists throughout the world now for over 150 years. The interest started in the U. S. after Drake drilled the first oil well in 1859. Interest greatly increased in the 1920's and 30's when systematic waterflooding started and increased again after Clark and his associates developed the hydraulic fracturing process around 1948. Many other recent interests in this subject have occurred due to earthquake and subsidence effects, the development of geothermal energy sources, subsurface liquid disposal, various in situ recovery processes, and most important, enhanced crude oil recovery. Fluid injection and production effects are relevant to several facets of crude oil recovery; hydraulic fracturing, waterflooding, firefloods, chemical floods, and all other secondary and tertiary recovery process. Many variables and schemes in oil recovery can be effectively evaluated through laboratory studies and mathematical modeling. However, many key process variables must be evaluated not only in the field, but in the specific reservoir under development. Such fundamental reservoir conditions as joints, fracture systems, layering and lenticularity of strata, and tectonic stress magnitudes, differences, and orientations are site specific and must be evaluated in each field along with oil saturation and permeability.

Rocks, more often than not, are naturally jointed and may have near orthogonal networks of fractures that vary from one stratum to another. The size may vary from small, closed, unconnected fissures, fractions of a millimeter long, to large, open fractures or faults several kilometers long. Whether such fractures exist and if they are open or closed needs to be determined as a part of secondary and tertiary recovery projects. True radial flow may be the exception, rather than the rule in most petroleum reservoirs.

This research was part of a comprehensive field, theoretical, and laboratory based research program to analyze and characterize petroleum program to analyze and characterize petroleum reservoirs and develop technology for mapping natural and hydraulically induced fracture systems. The subject of the present 25-minute film, "The Dynamic Pressure Response of a Petroleum Reservoir: A Field Case Study", deals with methodology and results from injectivity tests to delineate fracture systems in a petroleum reservoir. The general induced hydraulic fracture orientations were determined, but perhaps most interesting though, were the, far — field, dynamic pressure responses — the primary emphasis in the film. primary emphasis in the film.