Analyzing Well Performance X

Abstract

Abstract After a general discussion of fluid flow, this paper reviews the data which are necessary for well analysis. The acoustic liquid level instrument is described, well producing rate efficiency (with and without gas) is discussed and an analysis of downhole equipment is given. Introduction Analyzing well performance is an important step toward increasing profits by improving production techniques. The analysis is made by field tests and examination of well data. The acoustic liquid level instrument offers valuable information, because downhole pressures can be determined from the depth-to-liquid measurement. Fluid Flow (generalized) Fluid flow in a reservoir is caused by movement of fluid from a high-pressure area to a low-pressure area. Fluid flow into a wellbore occurs when fluids, present in the wellbore are removed so that the pressure is decreased. Then? fluid from an area of higher pressure flows into the lower-pressure wellbore (Fig. 1). Fluid flow into a wellbore is approximately proportional to the drawdown pressure, which is the difference in pressure between the higher pressure reservoir and the low-pressure wellbore. The greater the difference, the greater the fluid flow. Figure 2 represents some ideal cases of fluid flow in a reservoir. The lower the wellbore pressure the greater the inflow rate. Generally, in the past, the inflow rate has been assumed to be proportional to the drawdown pressure. This procedure is still used in wells which produce liquid without gas. Vogel(I) presents a curve for predicting flow rates in 2-phase flow (liquid and gas). This curve is shown on the Well Analysis sheet and should be used when predicting flow behaviour in wells making liquid and gas. Necessary Data for Well Analysis Four factors are extremely important in analyzing well performance:static bottom-hole pressure (or reservoir pressure),producing bottom-hole pressure,well test andpump capacity. For maximum withdrawal, the producing bottom-hole pressure must be low compared to the static bottom-hole pressure. A producing bottom-hole pressure of 75 psi is low compared to a static reservoir of 2300 psi, and practically all of the production is beng obtained. However, if the static reservoir pressure is 100 psi, approximately one-fourth of the production is being obtained. The well test must also be known. If the producing wellbore pressure is low compared to the static reservoir pressure, maximum inflow is occurring. However, if the maximum inflow is less than commercial production, action must be taken. Last, the pump capacity must be known. If the pump capacity is not matched suitably to the well's production, excessive wear and a mechanical loss of efficiency are occurring if the pump capacity greatly exceeds the production rate. A production loss occurs if the, pump capacity is less than the well's producing capacity. Note the importance of each item, by trying to determine the proper action on each of the wells in Table 1 when only one of the four items on each well is omitted.