Well Test Analysis in the New Economy (2003)

Abstract This paper provides a chronological history of the evolution of advancement in well testing techniques in order to examine how the technology has progressed to its present state. The first factors examined are those that strongly influenced technological development in well-test analysis. The next discussion concerns the problems that still require resolution, and finally, the authors will present what they envision for the future of well-test analysis. Introduction The origin of fluid flow through porous media may be traced back to the experiments run by Darcy during the 19th century to investigate the flow of water, a Newtonian fluid, through a bed of unconsolidated sand filter. This sand filter probably had a fairly high permeability. Darcy's equation was developed and became the basis for significant further development. It was not a great surprise to find that the equations governing flow of a Newtonian fluid in high permeability formations under laminar conditions are identical to those that govern heat flow in solids. The original idea of analyzing pressure vs. time data from a producing or shut-in well to obtain information on the producing stratum first appeared in the field of hydrology. Hydrologists were mainly interested in the behaviour of underground water flow in large aquifers. Shortly thereafter, The is(1) published his work on fluid flow in porous media, which included his point-source solution. Muscat(2) was probably the first to study a problem relating to oil reservoirs-the eventual static pressure behaviour of a shut-in well in a closed oil reservoir. When compared to the initial reservoir pressure, this new static pressure can be used to measure the quantity of hydrocarbons produced up to the time of the test. The need for reliable quantitative analysis has primarily been driven by economics since accurate formation permeability determination is needed for forecasting reservoir production. Initial reservoir pressure and drainage boundaries provide the information needed to determine the amount of hydrocarbon in place. However, determination of well condition (i.e., skin factor) is also necessary to predict how much expenditure will be needed to improve productivity. Since Muscat, literally thousands of papers have been published on the analysis of pressure tests. Numerous new tests have been devised to determine specific reservoir parameters. This explosion in literature was basically due to the ease by which pressure behaviour could be measured and the enormous value of the parameters calculated from these tests. In addition to the information mentioned, pressure tests can be used to estimate:How efficiently a well is completed;The need for and anticipated success of a stimulation treatment;The general type of well treatment desired; and,The degree of connectivity of one well to another. Modern well-test analysis started when Horner(3) and Miller et al.(4) presented their famous papers where semi-log straight lineswere introduced as the first technique for analyzing pressure tests. Within a few years, Van Everdingen and Hurst(5) and Moore et al.(6) introduced other fundamental developments with the concept of wellbore storage.