Producing the Well by a Compensated Pump

Abstract The production cumulative index (bbl/psi) or CPI, is the relation of the cumulative production versus the decline in the reservoir static pressure. This recorded index shows that the reservoir produces more bbl/psi static pressure as the reservoir static pressure decreases. The increase in the CPI can also be seen in a DST during the build up period. The increase in the CPI is explained by a better use of the reservoir energy when the production is lifted for shorter distances above the perforation. To increase the CPI it is necessary to produce the well by a compensated pump. This is a pump which is not driven by the intake fluid. Producing the well by a compensated pump increases the well efficiency in rate and cumulative production by about 200–250%. 1. Introduction The static pressure and the cumulative production are the two most important reservoir parameters. The static pressure represents the reservoir physical status, and the economical status is represented by the cumulative oil and water recovered during the production activity. Accordingly, maximizing the ratio between the recovered production versus the well static pressure decline, is the main goal of the production activity. This ratio is called the cumulative production index (CPI) and it is defined in bbl/psi. The well production recorded data shows that the CPI is variable and increases continuously as the reservoir static pressure decreases. Producing the well with the maximum CPI is the target of good production practice. 2. Recorded Well Production Activity a. The well cumulative production The oil reservoir is a huge sealed volume of permeable and porous rock. The reservoir is always sealed because after recovering the liquids from the underground the reservoir static pressure declines and actual never rebounds. The reservoir pores store the liquids and the permeability allows it to flow from the reservoir into the well bore. The only source of energy used to move the production through the pay zone and up into the well is the expansion of the reservoir fluids. Table 1, shows the Wilcox reservoir1 static pressure decline versus the cumulative production recovered: Table 1. Wilcox Reservoir, Cumulative Production Index The data shows a CPI increase from 1,850 to 17,020 bbl/psi or an efficiency increase of 920% versus a static pressure decrease from 3793 to 3277 or 86%. As the reservoir static pressure declined the well produced appreciable more oil per psi reservoir static pressure decline. Yates Field2 production history is another example of the increase in the CPI as the reservoir static pressure declined.