Lower Cretaceous Geology And Heavy Oil Potential Of The Lloydminster Area

Abstract

Abstract Lloydminster comprises the most southerly deposit of the Alberta-Saskatchewan Mannville heavy oil sand belt. Hydrocarbon entrapment is controlled in part by updip sand pinchout, but is related primarily to regional anticlinal closure associated with salt solution of the Middle Devonian Prairie Evaporite Formation. This area, with oil gravities ranging from 10 to 25 degrees API, differs from the rest of the "heavy oil belt" in that it has demonstrated primary recovery. Manllville sedimentation in the Lloydminster area was influenced by paleotopography and structure on the pre-Cretaceous unconformity surface. Widespread emergence accompanying the Paleozoic unconformity resulted in non-marine, mainly fluvial; deposition in the Basal Dina Clastic Unit. Maximum marine incursion occurred during Sparky time, and the remainder of the Mannville was a complex intertonguing of near-shore, deltaic and alluvial facies. "Widely developed channel fill deposits in the uppermost Mannville over much of the area indicate a return to emergent conditions which were terminated with transgression and inundation by the Colorado Sea. Higher sand content in the northeastert1 part of the area and mineralogy indicate that sediment source was the Precambrian Shield. The Mannville sands of the Lloydminster area contain more than 16 billion barrels of oil-in-place. The reservoirs that have demonstrated primary production and Were included ill this estimate comprise the Colony, McLaren, Waseca, Sparky, GP, Lloydminster and Cummings sands. The Sparky is the most prolific producer. The Cummings and Colony wilts have been minor contributors to date. Introduction The LIoydminster area, outlined in Figure 1, comprises a 10,750-square-mile (27,840 km2) rectangular block spanning the Alberta-Saskatchewan border between Townships 42 and 55 and Ranges 17 west of the Third meridian and 10 west of the fourth meridian. The border city of Lloydminster, the center of drilling and production activity, is situated in the north-center of the block. Edmonton, the provincial capital of Alberta, is 140 miles to the west. The Lloydminster heavy oil accumulation is the southern extension of a discontinuous trend of Lower Cretaceous bitumen and heavy oil sand deposits extending from Athabasca through Cold Lake to Lloydminster. Other ol sand deposits occur at Wabasca and Peace River. The Lloydminster pools, many of which are produced by conventional methods at the present time, contain oil ranging from 10 to 25 degrees API (1000-904 kg/m'). Enhanced recovery processes, where economical, have significantly increased production, with waterflood as much as doubling the 4 per cent primary recovery expected in some fields, Thermal recovery pilots have demonstrated considerably higher recoveries, but so far have proved to be marginally economic at best. This paper will outline the Lower Cretaceous Mannville depositional framework, illustrate selected depositional environments and describe an oil-in-place assessment for the area. History Lower Cretaceous oil was encountered in the L1oydminster area near Wainwright, Alberta in 1923. Although this discovery was soon followed by several significant shows, commercial production was not established until 1944, with development of the Silverdale Sparky sand pool 6 miles south of the city of Lloydminster, This led, in 1946, to the cons(ruction of the Husky refinery at Lloydminster and to a short-lived drilling boom that pushed production to nearly one million barrels in 1947.