Abstract
Unconventional or tight reservoirs are typically developed with horizontal well technology to effectively exploit the reserves, which could not have been economical with conventional vertical wells. These horizontal wellbores are completed with large multiple hydraulic fracture treatments across the entire length of the wellbore, to increase the reservoir contact per well. Well Productivity of these wells are proportional to the stimulated reservoir volume (SRV), which is the total conductive propped fracture surface area. For horizontal wells completed in the same reservoir this is approximated to the product of number of propped fractures and the conductive surface area of each propped fracture. Typically, hydraulic fractures are single planar vertical fracture characterized by fracture length, height, and fracture width. However, in case of unconventional reservoirs completed with horizontal wells, fractures are highly complex geometries which are mostly non-planar, multiple fractures sometimes creating a mesh network of fractures. Estimation of these complex hydraulic fracture geometry (HFG) dimensions has become very critical for any unconventional field development. Key dimensions are hydraulic fracture length, height, fracture network width and their orientation, which are required to assess the optimum configuration of fracturing, well completion, and reservoir management strategy to achieve maximum production.
This paper proposes a workflow using inter-well electromagnetic recordings to estimate and model all or at least two parameters of HFG in predominantly horizontal or nearly horizontal wells. The foundation of this workflow is the difference in salinity, or resistivity, of the fluid used for hydraulically fracturing the well and the resident fluid (hydrocarbon or formation water). The fracturing fluid is usually significantly more conductive than the resident fluid (hydrocarbon or formation water). This resistivity contrast between the two fluids is so significant as to demarcate the shape and boundary of hydraulic fractures and thus help in precisely modeling some or all parameters of HFG. The interwell recordings can be interpreted along a 2D plane between the two wells, using Crosswell Electromagnetics (Crosswell EM) acquisitions. This method is a significant improvement over existing acquisitions such as micro-seismic for estimating hydraulic fracture geometry. While micro-seismic considers both shear and tensile failure of the rock in estimating hydraulic fracture geometry, the methods discussed in this paper will allow demarcation of the boundary of only the contributing part of the hydraulic fracture, ignoring any shear failures or non-contributing rock breaks created during hydraulic fracturing.
