Wellbore Sinuosity and Its Effect on Production and Recovery from Horizontal Wells Along the Cummings/Dina Channel Trend in Senlac and Winter Saskatchewan

Abstract

Over 500 horizontal wells have been drilled into the Cummings/Dina channel trend between Senlac and Winter since 1990. These wells produce 13–14 °API oil with a gas free viscosity of 3600 cp from a depth of 700 meters. Production peaks at about 20 to 60 m3/d oil with 10% water and 1.5% sand. Oil production eventually declines as water cut increases. Sanding events can limit oil production rates and recovery. Wellbore trajectory control has improved significantly in the last 10 years, the latest improvement being ‘inclination at the bit.’ Selected wells were analyzed to determine the key factors between sinuosity and production rate and ultimate recovery, and the changes in the effect of these key factors over the last 10 years. Incentive and methodology for development of current flatter wells is discussed, and predictions for production from current flatter wells are given. Introduction Vertical well production of the Cummings/Dina channel that extends through the Senlac and Winter areas of Saskatchewan was uneconomic due to rapid water breakthrough from the active bottom water (Figure 1), with cumulative oil production varying from 150 to 700 m3. Beginning in 1988 horizontal wells placed high in the pay were demonstrated to be an economic alternative, resulting in rapid development of several commercial projects1–5. Production was improved by:increasing the well length,maximizing the standoff from the bottom water, anddecreasing inter-well well spacing. Eventually the water cut in all Senlac/Winter horizontal wells over bottom water rises until they become uneconomic (about 99% water cut). At that point only about 14% of the OOIP has been produced, and there is clearly a large incentive to further improve well performance. The ability to guide the bits while drilling early Senlac/Winter wells was at an early stage of development, and as a result the horizontal sections of early area wells had a relatively high degree of sinuosity. For this study sinuosity is defined as the vertical variation of the horizontal wellbore, described by the standard deviation of the wellbore trajectory standoff from bottom water. Less developed drilling and guidance methods also contributed to poorer than expected lateral placement of early Winter horizontal wells6. Some sinuosity was purposely built into a few early Senlac/Winter wells when the heel portion was purposely placed lower in the pay than the toe in hopes that gravity would aid flow into the area near the pump inlet. Sinuosity was also imposed by geology in some wells when shale sections deflected the bit up or down. Continued experience drilling a large number of horizontal wells and a decision to discontinue the practice of purposely drilling the wellbore lower at the heel has resulted in horizontal sections that were significantly less sinuous. Additional improvement in reducing sinuosity was still considered to be desirable and attainable. The most recent improvement at Petrovera's Senlac area wells was accomplished in 2002 by incorporating a reduced diameter ‘at bit inclination’ (ABI) tool. Subsequent sections discuss geology, numerical simulation, use of field data to define ‘sinuosity’ and ‘effective standoff from bottom water’, hypotheses of ways sinuosity affects Senlac/Winter horizontal well performance, and prediction of performance of less sinuous (flatter) horizontal wells.