Abstract

A joint venture project in the South Sulige gas field began in 2011 with the intent of developing efficient production in the field. The South Sulige gas field has two main producing formations, both with low permeability and porosity. Like many other tight gas sandstone formations in China, fracturing is necessary in order to get economic production in pad-drilling

To date, five wells horizontal and 60 vertical wells have been stimulated in the South Sulige field in this project including four vertical wells from an earlier campaign in 2008. The 2008 campaign had nearly 40% rate of premature screenouts and the first two wells in 2011 also experienced screenouts. Tracing the root of the problem to natural fissures in the formation, mitigation was taken that led to the elimination of premature screenouts since implementation. Post-frac well performances of the new wells have far exceeded production of wells previously drilled in the South Sulige field in 2008. This significant increase can be traced to a complete fracturing methodology that optimizes every step of fracturing design and execution.

The use of specialized multi-stage completions in the horizontal and vertical wells allows the operator to efficiently execute fracturing jobs while also minimizing downtime before flowback, cleanup, and ultimately production. Optimized fracturing designs minimize excessive height growth seen in previous work done in the field along with a new design workflow raise the potential production possible. The fluid design allows for rapid flowback and clean-up to minimize fracturing polymer formation damage. It also contains specific mitigation measures to combat the natural fissures observed in the formations throughout the field.

This paper will discuss the overall enhanced performance achieved through optimization of the fracturing work flow. The discussion will mainly focus on the different completion designs utilized for efficicent multi-stage fracturing in the horizontal and vertical wells, the optimized fracturing stimulation design and new design workflow, clean-up procedures to minimize formation damage, and mitigation of the natural fractures that are abundant in the formations of the South Sulige field.

Introduction

The Sulige field is located in Inner Mongolia and was discovered in 2001. The depositional environment is a braided channel system with many gas pockets. The South Sulige project began in 2007 with the drilling of two exploration wells and continued into 2008 with three more exploration wells. Using the information and experience gathered in this exploration phase, development of the field started in 2011.

The South Sulige field has two main producing gas formations, Shan1 and He8. They are tight gas sandstone formations, with low overall permeability and porosity. Hydraulic fracturing is required in order to obtain meaningful production from both of these formations. Pad drilling of deviated wells has been adopted as the main production method for this field. Horizontal wells are also being drilled and produced to investigate the potential benefits.

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