A Novel Technology for Locating and Evaluating Hydraulic Fractures in Horizontal Wells – Modeling and Field Results

Non-radioactive tracer tagged proppant technology has been used successfully in over 200 vertical wells to obtain fracture height and gravel pack coverage, but had yet to be modeled or tested in horizontal wells, where the borehole and fracture geometry is radically different. The purpose of this paper is to demonstrate the effectiveness of this new technology to locate proppant placement and to evaluate the efficiency of perforations and clustering in fracturing operations in horizontal wells. The new technology utilizes a pulsed neutron capture (PNC) logging tool to detect the tagged proppant, which has a high thermal neutron capture cross-section. Monte Carlo software is utilized to simulate the responses of different pulsed neutron measurements to vertical fracture planes along a horizontal wellbore. The tool responses were analyzed and the best PNC measurement parameters were determined for locating proppant placement in the fractures, and hence for determining perforation and cluster efficiency. A field test was the conducted to validate modeling results in a horizontal well with multi-stage fracturing operations. Modeling data and the field log example show that it is feasible to use the taggant and a PNC tool to locate proppant placement and determine the efficiency of perforations and clustering in horizontal wells. Furthermore, the analysis of the depth intervals of tracer signals and the known axial and radial resolutions of the PNC measurements show that the depth interval of tracer signals along the wellbore may provide a qualitative indicator of one or more of the following: (1) the presence of multiple fractures opposite perforation(s), (2) the angle between the wellbore axis and the fracture plane for ideal conditions (e.g. the more narrow the tracer signal along the log, the closer the fracture plane is to being perpendicular to the wellbore axis), and/or (3) proppant placement in the borehole region. Moreover, a new near-wellbore connectivity index has been developed based on identifying and using the most suitable PNC log parameters for the evaluation. The index indicates how well the induced fracture is connected to the wellbore at locations of all perforations/clusters. The field test demonstrated that this new technology met all of the operator's objectives, with tracer signals clearly observed in all stages. This paper will present the modeling work and the results from the field test. The new non-radioactive proppant tracer technology provides for the first time the ability to evaluate proppant location in horizontal wells without encountering the health, safety, and environmental issues associated with using radioactive tracers. The determination of proppant placement and perforation efficiency, and a near-wellbore connectivity index, can be employed to evaluate the success and effectiveness of individual perforations and stages, and to optimize future completion designs and processes for enhancing hydrocarbon recovery.