Hydraulic Fracturing of a Clay Rich Formation in Southern Chile: The Challenges & Successes
Authors: Britt L. K. , Otzen G.. , Guzman M.. , Kusanovic G.. , Alqatrani G.. , Dunn-Norman S.. 
Published: August 2016

The Glauconite Formation in southern Chile is an unconventional resource made up of approximately forty percent clay and glauconite, thirty-four percent feldspar, twenty-three percent quartz, and three percent tuff. Like many unconventional reservoirs outside the United States, establishing commercial production from the Glauconite Formation was difficult given the make-up of the reservoir, the availability of equipment and materials, and the logistics associated with drilling, completing, and fracture stimulating wells in a remote area like Tierra del Fuego in southern Chile.

This paper describes the effort to establish commercial production from the Glauconite Formation beginning with a couple of marginal wells in late 2011 through a nearly seventy-five well development by early 2016. As part of this effort, a basis of fracture design was established by developing a profile with depth of in-situ stress, Young's Modulus, and leak-off coefficient. These geomechanical assumptions were then tested and modified with core and pump-in data and used to make revisions to the fracture stimulation design. The designs were optimized to ensure that the critical fracture dimensions (fracture length, conductivity, and height) were achieved to maximize well performance.

Next, a data collection plan was developed to capture key information about completions, mini-frac analysis, fracture design and execution, fluid, proppant, and chemical additives, reservoir quality, and post fracture flowback and clean-up data. The database was then utilized to monitor the Glauconite fracture stimulation program to ensure that the basis of design for the fracture program maintains viability and to ensure that the appropriate equipment and materials were mobilized for fracture optimization and to meet the program objectives.

This paper focuses on the key elements of well completions and fracture stimulation practices as they apply to tight gas and unconventional formations by using the database to manage project risks and develop appropriate mitigation strategies. For example, preliminary fracture stimulation designs were based on initial reservoir permeability estimates of 4 md, however, the data collection plan incorporated a well test program which determined that the actual reservoir permeability was nearly one thousand times less.

Another example was the rock mechanics and geomechanical data derived from dipole sonic logs indicated little in-situ stress contrast and raised concerns about the ability to achieve the desired fracture dimensions. In addition, the log derived Young's Modulus was low and inconsistent with the core tri-axial compression and ultrasonic data as well as the on-site mini-frac net pressure data. As a result, a number of tri-axial compression tests were conducted and it was determined that the Young's Modulus was much higher than indicated from the logs. The collected data and monitoring program resulted in significant treatment modifications ranging from the small cross-linked stimulations conducted initially to linear gel, hybrids, and ultimately treated water fracture stimulations as equipment and materials became available. This work is beneficial as it:

Conducts an indepth well analysis and evaluation to develop a basis of fracture design, Builds a database of important reservoir quality, completion, mini-frac, fracture, and post fracture clean-up data, Utilizes the database to monitor the fracture design basis, manage material and equipment needs in a remote area, and to maximize well performance.