One of the major uncertainties in the analysis of unconventional well productivity is the estimation of the hydraulic fracture height generated during stimulation operations. This study was carried out in a well located in the Neuquen Basin, Argentina with main focus on the development of unconventional shale oil.
The strategy consisted in the application of two combined techniques based on different and independent physical principles for the estimation of the hydraulic fracture height. The initial technique consisted in the pumping of proppant which contains elements with great neutron absorption. Thereby, the presence of traced proppant is identified through the differences in the neutron absorption capacity before and after the stimulation at approximately 6 inches from the wellbore.
The second technique is based on the characterization of the anisotropy on the shear wave obtained by the dipolar sonic curve in two perpendicular directions. This acquisition should be carried out before and after the stimulation and it is sensitive in the area close to the wellbore. (Between 5 and 40 in)
Results from both techniques showed a reasonable good consistency in the results, thus allowing the validation of both methodologies.
The results also allowed defining intervals that act as barriers of the hydraulic fracture vertical growth. This permit us the optimization of the fracture design in other wells, thus minimizing the vertical over lapping of the fractures and maximizing the connectivity of the stimulated interval in the well. In addition, traced proppant was confirmed close to the wellbore in several intervals that together represent approximately 60% of the pay which represents a 170 m. To improve completion efficiency, this information can be used to place hydraulic fracture stages and define clusters geometry.
Finally, it could be determined that a set of factors allowed the control of the vertical growth of the hydraulic fracture with proppant in the proximity of the wellbore. The main control on hydraulic fracture height was the magnitude of the minimum horizontal stress. The presence of discontinuities in the rocks such as calcite veins volcanoclastic intervals and limestone beds may also play a role. These new data provide confidence on the current geomechanical model helping to optimize the upcoming stimulation operations in the area.
Authors: Alberto Cesar Ortiz and Damian Emmanuel Hryb, YPF; Joaquin Ramirez Martinez, Y-TEC; Raul Alejandro Varela, YPF
Paper number: SPE 179145-MS