Gas reserves were discovered in Tertiary age sands at Taglu in 1971. Difficult logistics, remoteness and delay in reaching potential markets precluded preinvestment in early and complete development drilling. Consequently the field has been delineated by a series of seismic surveys and six wells drilled over a span of seven years.

Estimates of the reserves are affected by variability in the seismic data used to interpret the structure of the field. Uncertainties also exist in each of several parameters used to calculate reservoir volume and hydrocarbon recovery. Imperial Oil Limited’s reservoir engineers and geologists have coped with these uncertainties and with continual addition and improvement in data by using a computerized reserves calculation program. The program accommodates ranges and probabilities for the various reserves calculation factors. Reserves estimates are displayed as ranges of reserve sizes with probabilities attached to specific values in the ranges.

The approach encourages disciplined examination of all reservoir data, reveals significant uncertainties in reserves estimates and provides a means to communicate these uncertainties and relate them to development planning and investment decisions.