Fracturing Microseismic Response in Turbidite Reservoirs in Tajin Field

Abstract

Selection of optimum well locations in heterogeneous turbidite reservoirs such as those found in Chicontepec basin, depends strongly on the description of heterogeneities—facies distribution and flow quality properties—as well as on the evaluation of the extent and orientation of propped fractures. Fracture growth propagation and orientation play an important role in visualizing and optimizing the drainage pattern of such complex reservoirs. To better understand the fracturing response of these formations and support the design of development strategies, several measurements of microseismic response under hydraulic fracturing were carried out in wells in the Tajin field. By deploying sensor on-tubing tools of treatment wells, microseismic data were recorded following the injection operation, yielded fracture extent and orientation and stress anisotropy. The computed hypocentre locations are distributed in a non symmetric cloud of seismicity with a global trend extending no farther than 195m away from the wellbore in the N20–30°E direction. Moreover, the acoustic emissions presented a remarkably consistent direction. Interpretation of location of shear-slip and acoustic emissions events is consistent with results provided by dipolar sonic image logging tools run on the same wells. Better understanding of reservoirs' response to stimulation leads the operator to review its fracturing practices for cost-effective reservoir stimulation. Numerical reservoir simulation grids for reservoirs in the zone were oriented according to the observed fracture trend. Introduction High volume of resources of hydrocarbons is found in several fields of Chicontepec canyon in Mexico, discovered in early 50 s. The low oil recovery, associated with poor understanding of the complex geology of Chicontepec submarine fan system, had historically discouraged the investment for the development of its fields. Recently, by using modern tools for geological description, such as 3D seismic, sequence stratigraphy and geostatistical applications, the understanding of turbidite reservoirs along the Chicontepec trend has been enhanced, particularly at Tajin field1. These low permeability (0.2 to 8 mD) and shaly set of reservoirs have been the focus of development at the southeast of this trend, where the quality of the produced oil ranges from 28 to 34 API. The location of Chicontepec trend is shown in Figure 1. More than 150 wells have been drilled in Tajin, and all are hydraulically fractured. Reservoirs are typical of low-permeability oil resources that require hydraulic-fracture stimulation for economic production. Fracturing practices are a key issue in the development of Chicontepec, and several aspects of the response of different facies to fracturing are still unknown. An intense program of several measurements of microseismic response under hydraulic fracturing operations is being applied in several wells of Tajin field. A better insight of field characterization of the created fractures along heterogeneous formations and the fractures-wellbore connection features provides the basis to optimize both fracturing design and drainage pattern. Geological Description As pointed out earlier, Tajin field is associated to a submarine fan system deposited under complex tectono-stratrigraphic conditions, where early deposition resulted in a multistoried reservoir system of complex strata architecture1. By a careful calibration of well log correlations and 3-D seismic interpretation a consistent resolution of the stratal geometries was obtained. These set of reservoirs is typically composed of channel complexes that are flanked by, and rest on, lobe sandstones that grade into distal fan and basin floor deposits. Facies variability resulted in a highly heterogeneous reservoir system which was characterized by mapping net sand and facies distribution along with other reservoir parameters obtained from well production and well testing.