Case Histories of Production Logging

In injection wells, the main purpose of the production log is to assign volumes or percentages of fluid to each interval taking significant amounts of it. In producing wells the objective generally is to identify zones contributing fluid specifically the quantity of each fluid and its respective entry. Introduction Production logging techniques can be broadly Production logging techniques can be broadly considered to include all types of subsurface measurements subsequent to the initial well completion, and there are undoubtedly instances when these measurements are taken before the actual mechanical completion. There are, practically speaking, two main categories of work into which most production logging falls: injection wells and production wells. The injection wells are generally receiving water as part of a secondary recovery, a pressure maintenance, or sometimes simply a disposal system. The injection medium may also be liquid hydrocarbons, gas (including air), or a combination of liquid and gas such as saturated steam. Whatever the injection fluid, the main purpose of the production log is generally to determine the injectivity profile, that is to quantitatively assign volumes or percentages of fluid to each of the intervals taking significant amounts of fluid. While the profile is being obtained, it is often important to check also for casing failures, packer leaks, faulty cement jobs and interzonal packer leaks, faulty cement jobs and interzonal migration. In producing wells the objective generally is to identify zones contributing fluidwater, oil or gas and more specifically the quantity of each fluid and its respective entry or entries. Static or shut-in wells may also be investigated with production logging techniques. A shut-in temperature production logging techniques. A shut-in temperature profile is a recognized means of qualitatively profile is a recognized means of qualitatively indicating where injected fluids have entered a reservoir. Recent advances in temperature logging present the possibility of identifying oil, gas or water in place in possibility of identifying oil, gas or water in place in the reservoir through the differences in their respective thermal conductivities. Approach to Well Analysis Injection Wells In many instances the relatively high injection rate (1,000 or more barrels per day) and a not too large casing or liner (7 in. OD or smaller) make the continuous spinner a highly suitable tool for attaining the injection profile. Where the continuous spinner is not suited, radioactive tracers can be resorted to; or under certain conditions the "packer-type" flowmeter can be used. A temperature profile is commonly run in conjunction with the spinner or radioactive tracer survey and is particularly useful in defining the presence of a static column if such exists. Producing Wells Producing Wells Since generally at least two phases (oil and water), are present in a producing well, a somewhat different approach must usually be made from that used in a single-phase injection well. If the well conditions and flow rates are suitable, the spinner approach may be used to determine the gross rates involved. (If substantial gas production is involved, the spinner should be useful in defining the entry point or points.) JPT P. 207