Characterization of Hydraulic Fracture Geometry in Shale Gas Reservoirs Using Early Production Data
Authors: Li Chunlou , Lafollette Randy , Sookprasong Andy , Wang Sharon 
Published: May 2016

Drilling long horizontal wellbores and completing wells using multistage fracturing are common practices in shale play development. One of the keys to enhancing production of these ultratight reservoirs is creation of a complex fracture system with very high surface area. Bi-wing fracture geometry parameters (length, height, width, and conductivity), are not sufficiently detailed to describe complex fractures. Instead, fracture density, unpropped and propped fracture conductivity, and stimulated reservoir volume (SRV) may be more appropriate parameters to consider in both fracture design and production modeling. Characterizing these parameters is challenging due to the uncertainty of natural fracture distribution, local stress changes, and the lack of granular reservoir description in three dimensions. Results of the current study show that post-treatment production data exhibit distinct features associated with various fracture systems and should be able to aid in describing the complex fracture system.

The primary objective of this work was to find correlations between early-time production signatures and the fracture network. First, production simulation models were set up with various combinations of secondary fracture distribution, primary fracture conductivity, and different sizes of SRV. Those models were used to generate synthetic production and load recovery data for different scenarios. Secondly, the generated production data were analyzed with diagnostic plots to identify characteristic features for different fracture scenarios. Peak production, earlier production decline rate, and time to reach peak production were also evaluated and correlated to various fracture geometries.

Results indicated that peak production correlated well with both SRV and secondary fracture density. Early-time decline rate was affected significantly by secondary fracture density. Time to reach peak production is impacted by fracture density, unpropped and propped fracture conductivity, and SRV. Diagnostic plots showed interesting features for various fracture scenarios, which may indicate complex flow regimes. This result needs further investigation.

Introduction

Although gas production from shales started a century ago, cost-effectively development of shale gas plays has always been a huge challenge in the gas industry. Shale gas reservoirs have ultralow permeability, usually on the order of 10s to 100s of nanodarcies. Conventional well completion techniques are not sufficient to achieve commercial production from such tight reservoirs. The two technologies that enable economic production of shale gas are long-lateral horizontal well drilling and multistage hydraulic fracturing. These technologies combine to create huge reservoir contact surface area by placing multiple transverse hydraulic fractures along long horizontal laterals.

Hydraulic fracturing has long been an effective technique for stimulating low-permeability reservoirs. To simplify fracture modeling, biwing, single-planar fracture geometry was often assumed from prefracture design to postfracturing evaluation. However, fractures in the real world have been documented to be much more complex. Especially for economic shale plays, hydraulic fracture interaction with natural fractures may result in complex fracture network development. The biwing fracture parameters—length, height, width, and conductivity—are not sufficiently detailed to describe complex fractures. Instead, another set of parameters—fracture density, unpropped and propped fracture conductivity, and stimulated reservoir volume (SRV)—may be more appropriate parameters to consider in both fracture design and production modeling.