Horizontal wells have helped in advancing the oil industry since it was first introduced in 19801.
As useful as horizontal wells have become, the need for careful preparation become even more imperative before drilling can begin. As a result. the oil industry wants to be sure that a horizontal well is the right choice and will be economical. This reassurance is obtained through the use of field simulators which simulate a well's operation and production. These computer simulations require careful preparation and accurate input data with the results being within accepted tolerances.
Engineers and oil companies also require a quick and easy method (plug and solve) of calculating production rates with "ballpark" results. Thus the question arises. what variables should be used and what models should be used? The answer is to simply use horizontal flow rate equations based on a few reservoir and fluid properties and reservoir and well dimensions. This paper will examine the result of a number of calculations using four horizontal flow rate equations (Borisov2, Giger3, Renard and Dupuy4, and Joshi5,6) and compare the predicted results to actual daily averaged oil flow rates and cumulative oil production figures.
Horizontal drilling and production started in Saskatchewan in the 1950's. These early oil wells consisted of only vertical wells. This conventional method of oil recovery initially met the production needs and oil recovery percentages ofthe time. Under favorable conditions (no formation damage, high initial reservoir pressure, no gas or water coning, etc.) vertical wells would recover no more than 60 percent of the original oil in place (OOIP) 1.
As oil needs increased and existing oil reservoirs were being abandoned before the reservoirs were depleted because no further oil could be recovered using conventional vertical wells or enhanced oil recovery (EOR) methods. another oil recovery methods were required The latest method is the use of horizontal wells.
The use of horizontal wells in Saskatchewan began in 1987 and have greatly influenced the province's oil production. As of December 1994, there were 1385 producing horizontal wells and 14138 producing vertical wells in Saskatchewan. 7 Although horizontal wells accounted for only 8.9 percent of the total number of wells, horizontal wells accounts for 33.8 percent of the total oil production. More specifically, the annual production ofheavy oil increased to almost 6 million m3 ofoil per year. The quarterly provincial oil production for horizontal wells steadily increased to where it is approximately a third ofthe total oil production. Figure 1 shows the provincial monthly oil production from horizontal wells with the total oil production broken down into heavy oil and light/medium oil production with a noticeable substantive increase in well production occurring in the middle of 1992.
Figure 2 shows the number of horizontal wells drilled per year in Saskatchewan and the type of oil being produced since 1987. The number of horizontal wells broke the 500 barrier in 1993. Figure 2 also shows the total cumulative number of horizontal wells in Saskatchewan and the number of wells drilled for heavy and light/medium oil.