XH27 is a heavy oil reservoir with a high oil/water viscosity ratio that incurs bottom water coning effects. To enhance the primary heavy oil production, 59 vertical wells with a 141-m square well pattern have been drilled since 1992. The highest primary oil production of 360 tons/day was reached in 1994. Starting in 1996, the reservoir fell into a significant production decline phase. The reservoir was on the brink of obsolescence in 2006 when a 93.6% water-cut discharge and a 0.26% annual oil recovery factor were recorded.
Based on detailed static reservoir characterization and updating of the dynamic reservoir model, the square vertical well pattern development strategy was shifted to a horizontal well drilling venture with a net-remaining-oil-distribution pattern. The major shortcoming to overcome was accurate placement of the horizontal section trajectory close to the reservoir top for the injector-producer wells. The thin oil-column target of less than 5 m added to the challenge.
To overcome these challenges, real-time well placement monitoring using high-resolution resistivity images, along with near-bit measurements, has been applied in all horizontal wells drilled. Clear identification of structural dips enabled the accurate reservoir model adjustment and allowed decisions on accurate trajectory corrections to be made while drilling.
A total of 33 horizontal injector-to-producer wells have been executed successfully. Three years from the inception of the new strategy, the average secondary production improved to 380 tons/day, which is higher than the best daily production during the course of primary production. The oil recovery is expected to double.
The application of the new horizontal well drilling pattern strategy, along with fit-for-purpose well placement technology, in the XH27 heavy oil reservoir has significantly increased the oil production and enhanced the recovery factor. The nearly obsolete heavy oil reservoir can be turned into an economically developed field.