DETERMINATION OF THE FLOWING BOTTOM-HOLE PRESSURE OF A VERTICAL WELL FROM SURFACE PRESSURE AND WELL PARAMETERS
1.1 BACKGRAND OF STUDY
Interpretation of data from Well test analysis have been based on the implicit assumption that the reservoir is a homogeneous single layer. However, the real petroleum reservoir, is a composition of layers with unique interlayer characteristics. The individual layers are usually separated from each other by an interface which could be either permeable or impermeable. Pressure behavior in this kind of vertically heterogeneous system is not necessarily like that of a single layered system and seldom reveals more than the average properties of the entire system. It is against this backdrop that this study became necessary. Well completion in such systems would be more instructive, enabling better reservoir and production engineering practice if detailed layer information is available at it prime. The petroleum industry is however interested in accurately calculating the pressure losses that occur for multiphase flow in the tubing and pipelines. Accurate predictions of pressure losses in pipes would enable proper design. Also, pressure determination in a production system in the petroleum industry is very important as it helps in the effective production of oil and gas from the reservoir but of all, the most important is the determination of flowing bottom-hole pressure as its knowledge helps in the determination of so many parameters needed for efficient production and also to avert early depletion of the reservoir. Its knowledge can also be used to prevent formation damage which could be caused by early sand production in the reservoir. Surface pressures often can be converted to bottom-hole values if adequate information is available about the wellbore system.
1.1.1 WHAT IS BOTTOM HOLE FLOWING PRESSURE
The pressure at the bottom of a working oil, water, or gas well (the Great Soviet Encyclopedia, 1979). The pressure measured in a well at or near the depth of the producing formation. For well-test purposes, it is often desirable to refer the pressure to a datum level chosen at a reference depth by calculating the pressure that would occur if the pressure measurement were made at the datum level rather than at the actual depth of the gauge(Schlumberger oilfield glossary). A knowledge of this pressure is fundamental in determining the most efficient methods of recovery and the most efficient lifting procedure, yet there is less information about these pressures than about any other part of the general problem of producing oil (Millikan and Sidwell, 1930). As earlier said, the bottom-hole pressure can be determined from surface pressures like the well head pressure if adequate information is available about the production system which can be easily gotten from well testing operations (Economides, 1979). Since the well head pressure and parameters are easily gotten from pressure transient analysis whose success depends on the accurate measurement or estimation of bottom-hole pressure (Omohimoria and Ayodele, 2013), it is therefore desirable and necessary to obtain the bottom-hole pressure from these data. This will be carried out in order to further highlight the advantages which is associated with having adequate knowledge about the flowing bottom-hole pressure of a reservoir.