Influence of Stress and Lithology on Hydraulic Fracturing in Hassi Messaoud Reservoir, Algeria

Abstract

Abstract Understanding the rock mechanics aspects of Hassi Messaoud (HMD) reservoir is extremely important, not only for hydraulic fracturing purposes but also for planning horizontal well drilling and completion. Analysis of the data generated from the hydraulic fracturing experience in Hassi Messaoud shows that fracturing is strongly lithology dependent. The magnitude and the orientation of the stress characterize the stress field. The stress magnitude in HMD is correlated to Young's modulus and shaliness. A new correlation is proposed relating minimum horizontal stress, shaliness and porosity. The stress field orientation in Hassi Messaoud is similar to that observed in other locations throughout Algeria. The maximum principal stress is in the azimuth direction between 135–140° azimuth, perpendicular to HMD anticline trend. The iso-fracturing gradient map of HMD structure confirms the compartmentalization of the reservoir into two main compartments. The eastern compartments, has a relatively low fracturing gradients, while the western compartment has very high fracturing gradients. The results of this study could be used in the selection of candidate wells for hydraulic fracturing as well as drilling horizontal wells. Introduction Impaired and low permeability formations need some form of stimulation to increase their production to an economically accepted level. Stimulation is usually performed by increasing the inflow area for fluids from the formation to the wellbore. Fracturing is used to overcome permeability restriction problems in oil and gas reservoirs, stimulating naturally low permeability or damaged formations. Warpinski et al1 stated that stress contrast is the predominant factor in controlling fracture growth. They analyzed in situ experiments that were accessible by mineback to determine the parameters controlling hydraulic fracture containment in layered formations. Beghoul2 used data from four-pad caliper devices: HDT (High Resolution Dipmeter Tool), SHDT (Stratigraphic High Resolution Dipmeter Tool), and BGT (Borehole Geometry Tool), in addition to the UBI (Ultrasonic Borehole Imager), to study the Ovalization in the TIMIMOUN basin (Algeria). He found the orientation of the major horizontal stress to be 134-145°. This direction was similar to that observed in GF-2, a well located in shaly sand reservoirs of Cambrian-Ordovician age within the Ahnet basin3. The measurement of in-situ stress is not straightforward. However, it can be estimated from logging parameters. In situ stress profiles are generally developed by use of the three following methods4:Measured in-situ stresses with microfracture (small volume) and/or minifracture (large volume) tests. In Hassi Messaoud, such measurements are obtained using minifracture pump in treatments before the main treatment.Log-based stress profiles, calibrated to measured in-situ stress data.Log-based stress profiles, calibrated with analogy, core, or other data. Because of the high cost of in-situ stress measurements, well logs are often used to estimate in-situ stress profiles. The literature provides many examples where microfracturing tests have been used, in combination with logs, to develop calibrated stress profiles for a field. Hopkins4 mentioned that in-situ stress profiles estimated from Lithological profiles, and calibrated to measured stresses from microfracture or minifracture tests provide good results. He illustrated this point with a Gamma ray Log correlation-based stress profile that is to be calibrated based on measured stress data and/or treatment data from comparable offset wells.