Applied Natural Fracture Characterization Using Combination of Imagery and Transient Information: Case Studies from Cambro-Ordovician Tight Sandstones of Algeria

Abstract

A majority of the world's oil and gas reserves are locked in tight, "unconventional", reservoirs. Without the presence of fractures (natural or hydraulic), these tight reservoirs with matrix permeabilities, usually less than 0.1md and porosities between 3–10PU, do not produce commercially. While hydraulic fracturing is widely used to improve the economic viability of wells, and fields to that matter, the presence of natural fractures plays the same role in improving the flow mechanics. As an industry, there are many tools available which characterize the properties of a created hydraulic fracture from both the predictive and evaluative standpoint. This is important in understanding the impact these properties have in increasing the production from a specific wellbore. Typically, we characterize these hydraulically induced fractures in terms of fracture height, length, width, and conductivity. These fracture characteristics are estimated using a variety of techniques including, pressure transients, production transients, micro-seismic, and various other techniques. However the ability to fully characterize natural fractures in terms other than pure qualitative (number of fractures observed, open or closed) has been limited in application and often only address conductivity. Based on case studies from Cambro-Ordovician tight sandstone reservoirs of the Hassi Messaoud field in Algeria, this paper describes methods that can be used to fully characterize natural fractures in terms commonly used for hydraulic fractures. With the application of combined imagery packages along with analyses of both pressure and production transient data, we now have the means to both understand the long-term impact of natural fracturing by associating quantitative properties that characterize both their locally observed (in-well) and far-field properties. Introduction Large oil and gas accumulations have been discovered in tight sandstone reservoirs of the Algerian Paleozoic sedimentary basins over the past fifty years. The worldwide trend and the drilling plans in Algeria confirm the strategic importance of these unconventional tight reservoirs for the gas production of the years to come. Recent advances in logging technology such as electrical and acoustic imaging used in combination with production data, transient pressure analysis and fracture stimulation techniques have opened new horizons in the characterization and the production of the challenging tight reservoirs of Algeria. Geology Located about 800 km South-Southeast of the capital Algiers (Figure 1) the Hassi-Messaoud field was discovered in 1956. With an original oil in place (OOIP) estimated at 41 billion barrels and a total production to date of 5.4 billion barrels, or 13.2% of the OOIP, this field is one of the biggest hydrocarbon fields in the world producing from Cambrian-age sandstone reservoirs with porosities ranging between 3 and 10 PU and matrix permeabilities typically less than 10md. The field currently produces approximately 400,000 BOP from more than 700 production wells.

Estimate of Permeability of Fracture Corridors/Networks: from Data Acquisition to Reservoir Simulations

“…With current advances in 3D seismic acquisition, processing, and interpretation, as well as in integrating core and log data, fracture characterization at reservoir scale has made significant progress, and various techniques have been applied to field scale cases (La Pointe and Hermanson, 2002;Massonnat et al, 2002;Ozkays and Minton, 2005;Shibasaki et al, 2006;Bounoua et al, 2008;Shen et al, 2008;Singh et al, 2008;Thakur et al, 2009). To have a truly predictive tool for fracture corridor/network permeability, one of the key challenges is to develop a fracture permeability model that can estimate fracture corridor/network permeability at a field scale based on its characterization.…”