Abstract

Abundant hydrocarbons have been produced from the Middle Triassic Halfway Formation of northeastern British Columbia; however, the facies relationships and geological history of this strata are poorly understood. To address these issues, 132 cores and well logs from 345 wells were examined from the Peejay Field of northeastern British Columbia in order to: 1) establish a depositional model; 2) identify the origin of all reservoir facies; and 3) construct an exploration model to better predict the trend of reservoir facies. Middle Triassic deposits of the Peejay Field comprise four west-southwestward prograding shoreface parasequences which form a progradational parasequence set. Palaeoshoreface deposits, referred to as Lithofacies Succession I (L.S.I), have been truncated and replaced with sharp-based cross-stratified bioclastic grainstone and litharenite tidal inlet fills, referred to as Lithofacies Succession II (L.S.II). Tidal inlet fills trend north-northwest to south-southeast and exhibit the best reservoir quality in the field. Successively younger parasequences are thicker and contain coarser grained lithofacies. However, the youngest parasequence (P.A. 4) varies laterally in thickness due to postdepositional erosion. Isopach maps and cross-sections through the Middle Triassic strata reveal the occurrence of a post-Halfway erosional surface that truncates successively older strata to the northeast. Superimposed on the northeastward thinning of Middle Triassic regional isopach trends are local north-south-trending thickness anomalies interpreted as post-Halfway block faulting. The combination of post-Halfway erosion and block faulting has resulted in reservoir facies preservation being completely controlled by structure. Based on reconstruction of the geological history, a hydrocarbon exploration model has been developed for the Peejay Field in order to predict the genesis, distribution and degree of preservation of reservoir facies.

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