The present study provides a comprehensive set of new analytical expressions to help understand and quantify well interference due to competition for flow space between the hydraulic fractures of parent and child wells. Determination of the optimum fracture spacing is a key factor to improve the economic performance of unconventional oil and gas resources developed with multi-well pads. Analytical and numerical model results are combined in our study to identify, analyze, and visualize the streamline patterns near hydraulic fractures, using physical parameters that control the flow process, such as matrix permeability, hydraulic fracture dimensions and assuming infinite fracture conductivity. The algorithms provided can quantify the effect of changes in fracture spacing on the production performance of both parent and child wells. All results are based on benchmarked analytical methods which allow for fast computation, making use of Excel-based spreadsheets and Matlab-coded scripts. Such practical tools can support petroleum engineers in the planning of field development operations. The theory is presented with examples of its practical application using field data from parent and child wells in the Eagle Ford shale (Brazos County, East Texas). Based on our improved understanding of the mechanism and intensity of production interference, the fracture spacing (this study) and inter-well spacing (companion study) of multifractured horizontal laterals can be optimized to effectively stimulate the reservoir volume to increase the overall recovery factor and improve the economic performance of unconventional oil and gas properties.
The objective of this study is to visualize the drained rock volume (DRV) and pressure depletion in hydraulically and naturally fractured reservoirs, using a high-resolution simulator to plot streamlines and time-of-flight contours that outline the DRV, based on computationally efficient complex potentials. A recently developed expression based on fast, grid-less Complex Analysis Methods (CAM) is applied to model the flow through discrete natural fractures with variable hydraulic conductivity. The impact of natural fractures on the local development of DRV contours and streamline patterns is analyzed. A sensitivity analysis of various permeability contrasts between natural fractures and the matrix is included. The results show that the DRV near hydraulic fractures is significantly affected by the presence of nearby natural fractures. The DRV location shifts according to the orientations, permeability and the density of the natural fractures. Reservoirs with numerous natural fractures result in highly distorted DRV shapes as compared to reservoirs without any discernable natural fractures. Additionally, the DRV shift due to natural fractures may contribute to enhanced well-interference by flow channeling via the natural fractures, as well as the creation of undrained rock volumes between the natural fractures. Complementary pressure depletion plots for each case show how the local pressure field changes, in a heterogeneous reservoir, due to the presence of natural fractures. The results from this study offer insights on how natural fractures affect the DRV and pressure contour plots. This study uses a fast grid-less and meshless high-resolution flow simulation tool based on CAM to simulate the flow in heterogeneous naturally fractured porous media. The CAM tool provides a practical/efficient simulation platform, complementary to grid-based reservoir simulators.
Despite emerging technology in the areas of unconventional forecasting, recovery factors are merely a fraction of its conventional counterparts. Unconventional reservoirs are characterized by their ultra-low permeability. It is to be noted that traditional decline curve analysis (DCA) is not best suited to forecast unconventional reservoirs. This is due, in part to a variety of reasons the most important being lengthy transition zones from transient flow to boundary-dominated flow which is highlighted in this paper via the usage of diagnostic plots.
The objective of this paper is to compare the production performance of volatile oil reservoirs, generated from a commercial compositional simulator, by using simple decline models used in the industry. Fluids with different initial gas to oil ratio (GOR), due to different fluid composition, was simulated for a period of 30 years. Oil rate was forecasted by assuming different lengths of available production history. We present the application of diagnostic plots to identify different flow regime. The results from our study showed that the duration of linear flow period and the transition from linear to boundary dominated flow varies drastically based on the initial fluid composition. With respect to the decline curve analysis performed, a hybrid decline curve model was used to model different sections of the production profile. Since we are analyzing volatile oil reservoirs, the biggest challenge in performing traditional DCA is the effect of multi-phase flow behavior. So, use of hybrid decline model results in a better production forecasting compared to a single decline curve.
With the advent of the shale boom, many oil and gas producers struggle to forecast unconventional reservoirs effectively. We believe that this paper serves to further elucidate the theory and application behind the concept of unconventional forecasting.