Abstract

Precise characterization of unconventional reservoirs is necessary not only for proper comprehension of heterogeneity, but also for adopting appropriate drilling and completion strategies. Though often deposited in laterally extensive facies, these mudstones vary sufficiently to be characterized by nondescript methods. This paper proposes a multidisciplinary approach for characterizing these reservoirs. The workflow involves petrophysics, geology, and geomechanics, and provides comprehensive characterization and useful parameters that can be used for designing completion strategies.

In this multidisciplinary approach, the reservoir is characterized based on its geologic and petrophysical merits and is also closely studied in terms of geomechanical properties, organic pore volume, and type of reservoir fluid present. The mineralogy of these reservoirs, and particularly that of the clays present in the matrix, dictates the nature and amount of bound water present that could influence the reservoir deliverability. Natural fracturing and the complex geometry of pores, along with the secondary porosity induced from diagenesis, also play important roles in the producibility of these reservoirs. With this approach, an attempt is made to qualify these secondary pore systems and determine their impact on the reservoir deliverability.

One main challenge in characterization of unconventional mudstones is the impact of kerogen content on conventional log signatures. Hence, to achieve proper characterization, it is important to obtain reservoir parameters such as porosity, which is independent of lithology, and parameters such as water saturation and kerogen volume, which are independent of conventional log measurements.

The integration of geomechanical properties with geologic and petrophysical interpretations is one key aspect of this workflow. A three-dimensional (3D) stress analysis [vertical transverse isotropy (VTI)], when integrated with petrophysical parameters, provides important insight into horizontal placement and completion strategies.

Currently, successful completion of unconventional wells requires precise characterization of reservoirs through integration of multidisciplinary datasets to validate crucial reservoir parameters from measurements independent of one another. Obtaining and incorporating that information during various stages of well planning (horizontal placement, hydraulic fracturing, etc.) helps maximize the likelihood of a successful well.