Sand Fracturing The Slave Point Carbonate
Authors: MacDonald R.G. , Frank K.E.J. 
Published: March 2010

The Slave Point carbonate in the Red Earth – Loon Lake area of Alberta is generally regarded as a secondary prospect to the area's prolific Granite Wash zone. Since late 1980, large sand fracture treatments have been used to stimulate newly completed and producing Slave Point zones with some impressive production results.

Post frac analysis of these wells with the use of a hydraulic fracture simulator has confirmed the effectiveness of the sand fracturing techniques, as well as the need to integrate geologic factors, reservoir characteristics and economic payout with fracture treatment design.

This paper will discuss reservoir parameters, fracture geometry, economics of the treatments and the evolution to the present choice of fluids, rates and sand concentrations of the hydraulic fracture treatments.

Introduction

The Slave Point carbonate possesses a complex lithology, with "reer "or "platform " oil production potential: This limestone zone has in-situ permeability and porosity that seldom exceeds 5 md and 10%, respectively.

Because the Slave Point is historically the second zone considered during the initial drilling of Red Earth, DST and core data is not available. In addition, well tests are difficult to execute on these law permeability, pumping oil wells to gain further reservoir data.

Computer simulation offers a new opportunity to evaluate the Slave Point. Well production histories can be matched by a hydraulic fracture simulator to evaluate the reservoir's range of parameters in the absence of other well information.

The hydraulic fracture simulator is a numerical model that combines a reservoir simulator with crack generation, proppant transport and fluid rheology models(1,2). It has the capability of simulating three-dimensional, two-phase flow in the reservoir simultaneously with the propagation of a two-wing vertical hydraulic fracture. Proppant transport and settlement, as well as fluid leak-off from the fracture to the reservoir, are calculated during the pumping and closure sequences of the treatment. Stress in the reservoir and on the fracture proppant is calculated throughout the simulation, enabling the transmissibilities to vary continuously as pressures in the reservoir change during production.

With this tool, and the application of the history match technique, it is possible to evaluate the reservoir and any subsequent stimulation treatments. Adjustment to reservoir parameters (within the limits of available data) is made until the simulator calculated production matches the actual production decline. With a history match, the reservoir and fracture are verified as accurate. This reservoir model can then be used to evaluate stimulation treatments.

Slave Point sand fracs have evolved from a field trial to a computer-assisted design procedure. The most important considerations of present carbonate sand fracturing techniques will be discussed.

Geology

The Slave Point Formation is a carbonate zone found in the north-central and northwest area of Alberta. The Slave Point is thickest in northern Alberta and it thins progressively southward to Red Earth. The Peace River arch marks the western extent of the Slave Point(3), shown in Figure 1.

The Slave Point is primarily limestone, only slightly dolomitic. Its complexity has been described in the Lubicon area, where four facies developments fringe a granite basement high(4).