An optimum pumping unit installation can be made for high volume sucker rod lift wells. Using three phase inflow performance relationships, vertical flowing gradients and predictive sucker rod design programs the ideal setting depth of the pump and the size of the equipment can be selected.
The typical sucker rod design involves using a predictive computer program (API or wave equation) to generate possible solutions for the pumping unit installation. If the production predicted by the program is acceptable, without exceeding the equipment limitations, then the design is completed. The pump is usually set as deep as possible to maximize production. The rods and pumping unit are sized by assuming that the well is pumped off so that the equipment will not be overloaded in the future. This will result in larger equipment being installed on the well. These design philosophies are based on experience from wells with low bottomhole pressure and low productivity. However, in reservoirs with strong water drives, the desired production can often be achieved by setting the pump higher in the wellbore while installing smaller lift equipment.
By combining the inflow performance relationship, vertical flowing gradients and pumping unit performance data, the optimum design of high volume sucker lift can be made. This process can optimize the lift equipment under various limiting conditions such as maximum water production or a requirement to utilize existing equipment. This paper details the procedure for optimizing the sucker rod lift equipment.
The first step in optimizing the pumping unit installation is to establish the inflow performance relationship (IPR) of the well. Before the pumping unit installation can be optimized, an estimate of oil, water and gas production for various flowing bottomhole pressures must be made. The most common methods of calculating the IPR such as Vogel, Fetkovich, Jones, Blount and Glaze, Klins and Majcher and Uhri and Blount are for solution gas drive reservoirs. These methods are for two phase flow: oil and gas. This paper deals with wells producing three phases: oil, natural gas and high volumes of water. Three correlations for calculating three phase inflow performance are presented below.
In the first method, Brown presents a solution developed by Petrobas to calculate three phase flow. This method requires a single oil and water test, measurement of the flowing bottomhole pressure during the test and knowledge of the average reservoir pressure. This correlation uses a Vogel type equation for the oil IPR and a constant productivity index (PI) for the water IPR. The oil and water fractions are held constant for all flowing bottomhole pressures.