Abstract

The introduction of computerized data acquisition and treatment analysis units to hydraulic fracturing has proven to be a very powerful tool to assist in both treatment design and treatment execution. Real-time displays of important parameters allow for on-site analysis of pressure behaviors as well as providing an excellent means of quality control. Data stored on floppy discs has made detailed post-treatment analysis and job to job comparison practical and shown Some excellent results.

The Gilwood sandstone in the Mitsue area has often shown very favorable production responses to hydraulic fracturing, although the unpredictable properties of this formation have made reliable treatment design and execution almost impossible. Many treatments have screened out prematurely, yet post-treatment results tended to show little difference between these wells and those in Which treatments were pumped to completion. For these reasons. it was very important to gain more knowledge of this formation in order to improve stimulation techniques.

By using a real time data processing unit on several treatments, it was possible to identify the following properties which made stimulation design difficult.

  1. Poor fracture height containment

  2. Very high and unpredictable fluid loss

  3. The presence of high permeability streaks

  4. Extremely variable productivity throughout the Mitsue field

Once identified, these properties could be taken into account to better design subsequent treatments providing improved stimulation performance in the area.

Introduction

The Gilwood sandstone is a member of the Watt Mountain formation. Kramers1 (1967) summarizes the composition of the Gilwood sandstone as follows:

  1. Color-Pale yellowish gray to light gray

  2. Grain Size-Fine to coarse grained

  3. Angularity-Angular to rounded

  4. Sorting-moderately well to poor

  5. Textural maturity- submature to mature

  6. Feldspar-8 to 28% increasing to north-west

  7. Rock fragments- less than 1%

  8. Cement- Sillca, carbonate, anhydrite (3.2 - 32%)

  9. Porosity- 0–16% depending on cement distribution

  10. Classificatlon- Mainly feldspathic sandstone

Kramers1 (l967) concluded that deposition of the Watt Mountain formation took place in a near shore environment that ranged from shallow water marine to possibly continental nearer the Peace River High." To further elaborate on the above it was suggested that the sandstones in the Mirsue area could have been "deposited by a distributary system that produced either a compound delta or was several streams producing a coalescing coastal flood plain type of environment" (Kramers 1).

As a result of the above, the Gilwood sandstone is apparently made up of a network of high permeability sand stringers, surrounded by lower permeability sands, shales and mudstone. This along with the irregular porosity distribution due to the large amount of cement present can hinder both exploration and production.

In the past, wells in the Mitsue area that were fracture stimulated frequently sanded off early in the treatment as a result of pad leak off. It was initially thought that this was a result of high permeability caused by natural fracturing.

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