Hydraulic Fracture Height Estimation in an Unconventional Vertical Well in the Vaca Muerta Formation, Neuquen Basin, Argentina

Abstract

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 overlapping 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.

Detectability of smart proppants traced with gadolinium and samarium in the Vaca Muerta formation

“…The Vaca Muerta formation is the most relevant reservoir for unconventional hydrocarbons production in Argentina (Ortiz et al, 2016) and it is ranked second and fourth in the world for shale oil and shale gas, respectively (EIA, 2013).…”

“…The reservoir, located in the Neuquén basin, has been extensively described in (Suarez et al, 2015;Stinco and Barredo, 2014;Sagasti et al, 2014;Suarez et al, 2013) and references therein. This formation is represented by organic shales and marls with thickness varying from 25 to 450 m (Ortiz et al, 2016;Stinco and Barredo, 2014).…”

“…Vaca Muerta formation shows different facies related to depositional characteristics and its position within the basin, with total organic concentration (TOC) variations from almost 15 % at the base down to less than 2 % to the top. Values of porosity range from 9 to 13 porosity units (Ortiz et al, 2016). Limestone layers, calcite veins and calcified and non-calcified volcanoclastic beds are also present (Ortiz et al, 2016).…”

High macroscopic neutron capture cross section ceramics based on bauxite and Gd2O3

“…After the well stimulation process, it is highly desirable to know the fracture geometry and proppants distribution in it. Recently, methods to identify proppants in induced formation fractures have been proposed (US Patent 8,234,072 B2, US 8,648,309) and applied [6][7][8][9] [10][11][12][13][14][15]. These methods require the incorporation of a suitable high thermal neutron capture element, such as gadolinium or samarium, into the proppant grain during the ceramic manufacturing process.…”

“…Up to date there is only one traceable proppant (ceramic) available in the market which uses gadolinium oxide [17,18]. The technology has been successfully employed over 200 vertical wells in field operations in the last decade [7][8][9][16][17][18][19][20].…”