Inferences of Two Dynamic Processes on Recovery Factor and Well Spacing for a Shale Oil Reservoir
Authors: Rodriguez Alfonso 
Published: August 2019

Current industry trend of "manufacturing" approach to develop unconventional shale reservoirs would make the journey to reach an optimized solution long by considering the historical deployment of current and emerging technologies in the last decade in North America. The basic premise is that "it is not possible to optimize what it is not fully understood". Significant research and the deployment of multiple technologies by the industry, academia and governments around the world are contributing to improve our understanding of how to develop unconventional shale reservoirs. However, key challenges remain that are fundamental to be addressed to reach an optimized development and it would require a " different mindset" to be able to develop effectively unconventional shale reservoirs. Technologies deployed to develop unconventional shale reservoirs should be subdivided based on two dynamic processes. The first dynamic process is occurring during the hydraulic fracture generation and the second dynamic process is during the production phase. The first dynamic process plays a vital role that influences the second dynamic process. The main scope of this paper is to assess recovery factor distribution and well spacing for a shale oil reservoir considering both dynamic processes.

The Current work is based on the utilization of Kinetix-Intersect; modeling results were compared to Stimplan for a selected stage and rate transient analytical results. Highly complex heterogeneous hydraulic fractures are created during the first dynamic process resulting in variable areal and vertical pressure distribution and flow anisotropy occurred during the second dynamic process or production phase. Kinetix-Intersect model results indicated a variable recovery factor distribution after 30 years of production, 8.9% in the near-wellbore dynamic nano-darcy region, 2% and 1.7 % for the inter-hydraulic fracture and external feeder regions respectively for the shale oil producer evaluated. Kinetix-Intersect model results indicated that about 2/3 of total hydrocarbons produced are contributed by the near-wellbore dynamic nano-darcy and inter-hydraulic fracture regions and the remaining 1/3 by the external feeder region. Acknowledging the variability of recovery factor distribution and pressure depletion associated to the producer drainage area should be the basis for the potential implementation of Enhanced Oil Recovery (EOR) techniques.

For the shale oil producer analyzed in this study, current model results indicate an asymmetrical shape drainage area and a variable well spacing in the range of 350 to 400 meters based on displacement efficiency and non-uniform recovery factor distribution. From a pressure depletion perspective, the estimated well spacing should be at least 400 meters. However, an optimum full field development would require the consideration to implement variable well spacing and tailoring completion and fracture treatment designs based on timely identification of areal and vertical heterogeneity of static/dynamic reservoir and geomechanical drivers to optimize project economics. Streamlines were used as a drainage qualitative indicator tool to help defining well spacing criteria. In summary, the route to attain better recovery factors for unconventional shale oil reservoirs commence with the understanding and quantification of the areal and vertical pressure depletion distribution along the horizontal section of the parent wells based on both dynamic processes; this is a vital input to define a suitable well spacing and effectively deploy adaptable drilling, completion and fracture treatment designs to reduce the occurrence of detrimental ‘Frac –Hits’ and improve oil recovery for future parent-child wells. The current expected recovery factors for unconventional shale producers are suboptimal with natural depletion and the need to increase the recovery factor with the deployment of EOR technology is paramount.