Paper: Stimulation Fluid Factors In A Study of Formation Damage In Several Morrow Sands

Coreflow studies, X-ray diffraction, and a variety of other investigative techniques have been used in the study of the design for stimulation fluids for a number of years. Recently, the concern for the design of non-damaging stimulation fluids to treat "problem", well-consolidated, low-permeability low-porosity sandstone reservoirs has heightened. A typical example of a problem sandstone in the Pennsylvanian age group is the overall Morrow sand. The Morrow is considered to be in southeastern New Mexico, the Texas Panhandle, the Oklahoma Panhandle, and west-central Oklahoma at varying depths. The heterogeneity of the Morrow is displayed by the inclusion of laboratory investigation data which are necessary to point out the reasoning for the fluid types recommended in the Morrow in the abovementioned areas. Following presentation of the investigative data, various case histories will be presented to substantiate the successful use of the recommended fluid systems in what has been labeled by operators, problem areas. The significance of fluid pH, low surface/ inter-facial tension, iron chelation, and low-residue gelling materials, has been the premise for the treatment type which is being recommended for Morrow sections in the majority of the areas documented. Core data point to a general need to encounter or avoid specific components in the matrices of the Morrow sands. Core studies have shown that a recently developed combination of a weak HC 1, weak HF acid system (3%HC 1 plus 1.2 HF) and a highly effective fluorocarbon surfactant provided significant improvement in the ability of a fluid to successfully act on the inherent problems within the matrices of most Morrow sands. This implies that the Morrow is a candidate for damage, regardless of the considerations made to complete and/ or stimulate it with "so-called" non-damaging fluids such as "clean" gels or condensate. The inherent potential for damage initiated by stimulation lay in the strategic location of migrating fines, iron compounds and extraneous clays within actual permeability and porosity. To avoid particulate matter damage with even minor penetration from commercially available fluid-loss additives for either oil or water frac systems, the amount used should be carefully considered. The core studies which were run in the Morrow sections listed in Table 1 were intended to indicate the design which was most compatible and successful from the standpoint of encountering matrix conditions, and not to determine volumes to be utilized in treatment. The engineering aspects of these designs for the field followed contemporary computer methods. The flow tests were run with constant volumes for relative comparison purposes to show that significant pore volume concentrations could provide correlating data with actual recommendations followed by treatment." The scanning electron microscope has been useful in identifying the location of potentially damaging particles within the permeability and porosity of the Morrow which have been documented by X-ray diffraction.