As part of a larger project, the relationship of horizontal well productivity and reserves to geology and reservoir properties has been examined at the Winter and Senlac heavy oil fields in Saskatchewan and at the Pembina field in Alberta.
In the Winter Cummings Sand pool, vertical wells have not been successful in exploiting 36 million m3 of heavy oil that occurs in a thick sand bar. Horizontal wells have average production of 22 m3/well/day and indicated ultimate reserves of 15.000 m3/well in the portion of the pool studied. Developed reserves are strongly dependant on standoff of the wellbore above the oil-water contact with at least 4.5 m of standoff required to produce beyond payout.
In the Senlac Cummings-Dina pool, vertical wells are unsuccessful whereas horizontal wells are producing heavy oil at economic rates, The main sand body is possibly an estuarine deposit that occurs in a channel between continental and marine depositional realms. In the portion of the field studied, horizontal wells have ultimate reserves of 25,000 m3/well. Standoff of the wellbore above the oil-water contact IS not an obvious control of reserves developed but there is a positive correlation between reserves and wellbore length.
Success of horizontal wells in the Pembina Cardrum light oil pool is strongly dependant on geology and reservoir properties. Horizontal wells located In areas of thick permeable conglomerate and permeable sandstone are successful whereas those drilled in low permeability reservoirs are failures.
As part of a larger study, the authors have investigated the results of horizontal drilling in three sand pools in western Canada, The three pools are: Winter Cummings Sand Pool a producer of heavy oil in the L1oydminister area of western Saskatchewan Senlac Cummings-Dina Sand Pool which also produces heavy oil near L1oydminister and the Pembina Cardium Pool an important producer of light oil in western Alberta (Figure I).
Winter and Senlac each have original oil-ill-place in occurs In thick sands having excellent reservoir properties. Both pools have extensive bottom water zones so that water coning has been a severe production problem in vertical wells because of the adverse mobility ratio of oil to water. Generally vertical wells have been uneconomic whereas there has been successful cold production from horizontal wells.
The Pembina Cardium light-oil pool was discovered in 1953 and contains approximately 250 million m3 (1.600 million STH) of recoverable reserves. The Cardium oil reservoirs are of interest for horizontal development because or their vast size and because there is a large amount of unrecovered oil-in-place despite secondary recovery being in place for a long period of time. At the time this project was undertaken. Amoco had drilled several horizontal wells in the study-area in the southwest part of Pembina field. Eight of these horizontal wells, drilled in areas of poor reservoir were unsuccessful whereas a horizontal well drilled in an area of good reservoir appears to be economic.
This report is drawn from a larger study conducted under the sponsorship of Saskatchewan Research Council.