Fracturing Fluid Improvements For Gas Wells In Canada
Authors: Black H.N. , Ripley H.E. , Beecroft W.H. 
Published: March 2010

Some of the Upper Cretaceous gas producing formations in the Alberta area are extremely water-sensitive, low permeability, shaley, marine sandstones. Offsetting the low porosity, permeability and reservoir pressure of these shallow gas sands are their widespread distribution and uniform characteristics over hundreds of square miles. With recent increases in the price of natural gas, and improvements in drilling and completion technology, the interest and drilling activity in these gas-producing formations has increased.

Laboratory research and field operations have cooperated to develop better chemical additives for hydraulic fracturing fluids. These additives help reduce clay swelling and excessiveplugging caused by the migration of formation fines.

Regained gas permeability tests using formation cores show the advantage of using these additives. Scanning Electron Microscope (SEM). X-ray diffraction, petrographic coreanalysis and fluid immersion tests were evaluated in this research study.

Field results for wells fractured with improved fluids are included. Better gas production has resulted from wells fractured with these new fluids.

Introduction

The area of interest in this study is in the Alberta Basin in Western Canada. The three main provinces included in the basin are British Columbia, Alberta and Saskatchewan. The first commercial gas production in Alberta began in the Medicine Hat area in 1890,(1) Since that date, many advances have been made in Canada in completion and stimulation techniques. The intent of this study is to review some of the most recent improvements in these areas of technology.

A study(2) of the Suffield Block in the Alberta Basin shows a stratigraphic column with sediments ranging from Pleistocene through Cambrian which covers over 7,000 feet (2.133 metres), including the most productive Upper Cretaceous. The Upper Cretaceous, from the base of the Fish Scales Formation to the Milk River Formation, is about 1,200 feet (366 metres). The lithology consists of a thick marine shale containing several sandstone and siltstone zones which provide the majority of the gas production. Three of the main producers here are the Milk River, Medicine Hat and Second White Specks sands.

The Medicine Hat and the Second White Specks sands are offshore bar types which were deposited in a high-energy environment.Reservoir qualities are generally fair to good, with permeabilities ranging from 0.1 to 5 millidarcies.

The Milk River Formation, which is usually thicker and more widespread than the other two zones, consists of finer-grained sediments. These sediments were transported beyond the high-energy environment and deposited in quieter waters offshore resulting in thin-bedded sands with high silt content interbedded with shale. The better Milk River sands may have penneabilities ranging from 0.1 to 1 mi11idarcy. The porosities vary from 10 to 15 per cent in the better sand stringers. The net thicknesses of productive Milk River Formation may vary from about 1 foot to 30 feet thick (0.3 to 9 metres), with as much as 300 feet (90 metres) gross thickness.