Seven gas wells in the Grizzly Valley Area, B.C., were tested in either the Nikanassin (Jurassic) or the Halfway (Triassic) formations for purposes of estimating reservoir parameters and well deliverability potential, and also for proving reserves. Two types of tests were conducted, these being of either the modified isochronal (multi-rate) type or the extended flow (single-rate) type. A significant departure from the conventional design and conduct of these tests is presented.
Some pertinent information on reservoir geology, well completion and test sequences is provided as background material. The interpretation and results of the well test data are presented with particular emphasis on the validity and usefulness of the single-rate tests as compared to the multi-rate test. Various related matters and problems experienced during testing are discussed. Recommendations for future testing of similar wells are also presented.
Illustrations at end of paper.
The Grizzly Valley Area in north-eastern British Columbia has been the scene of considerable gas exploration activity in recent years. The first indications of gas in the Monkman Pass area were obtained with the drilling of a well in 1955, but due to poor market prospects any significant exploration was curtailed until the early 1970's. However, an ever-increasing demand for gas, coupled with rapidly escalating gas prices created a favorable climate for extensive exploration activity which has culminated in a decision to construct a pipeline into the Grizzly Valley.
The Quasar et al properties extend for approximately 35 miles from the Wolverine Field in Block K, 93-I-15 to the Ojay Field in Block F, 93-I-9 with initial estimates of proved, probable and potential gas reserves in excess of 1 Tcf. A major proportion of these reserves are attributed to the Nikanassin and Halfway formations, although some other horizons that have not been fully evaluated are also included in this estimate. The general area of interest is shown on Figure 1.
During 1976 −77, Quasar initiated a gas well testing program in the Grizzly Valley Area. The objectives of the test program, the types of tests conducted on several wells, the results of test interpretation and a significant number of related aspects are discussed in the following sections.
The ‘primary’ objectives of the gas well testing program in the Grizzly Valley Area were to prove the existence of the postulated gas reserves in the Nikanassin and Halfway formations and to provide some basis for establishing the initial gas deliverability potential of most of Quasar's wells.
To achieve these objectives, several ‘secondary’ objectives, towards which the subject matter of this paper is directed, were defined as follows:
Determination of initial reservoir pressures,
Determination of the effective permeability thickness and the extent of damage of improvement exhibited by each well,
Determination of well deliverability and deliverability parameters,
Determination of the type of system penetrated by each well, i.e. matrix or matrix-fracture system,
Determination of the ability of the tight matrix to contribute gas in commercial quantities,
Estimation of gas reserves proven by test or indications of depletion due to test production.