Horizontal well design in Wafra field, Ratawi Oolite reservoir

This paper presents the selection and design procedures for a side-tracked horizontal well in this semi-depleted reservoir. A commercially available black oil simulator was modified to account for the horizontal well simulation. After the pressure and production history match of the 40-year period, horizontal well production forecast was made. Different horizontal well lengths, positions and bottomhole flowing pressures were used to study the production performance. Production rates, cumulative oil production and water oil ratios are resulting parameters in selecting the most suitable scenarios for decreasing pressure drawdown, and possibly improving the recoverable reserves. Results indicate that: 1) A 2000-foot horizontal well completed in the upper layers with maximum stand off from the water-oil contact would produce almost seven times more cumulative oil in 5 years than the vertical well in the same location. The potential starting oil production rate of this horizontal well is eight times that of the vertical well; in actual operation, we would limit pump sizes to produce the oil at less than the maximum capacity calculated. 2) A 2000-foot horizontal well completed in the zone closer to the oil-water contact would lead to less oil and more water production. 3) When the length of the horizontal well is increased to 3000 feet, the five-year cumulative oil production is increased by 15%, and more importantly, the cumulative water production amounts to only one quarter of that of the 2000-foot case. This is the recommended case for drilling a horizontal side track for this well.