The general purpose of Production Logging is to evaluate the behavior, and type, of fluids within the wellbore during either production or injection operations. Although there are a number of logging services available to the industry which provide this type of information, a standard group of production logging tools will include a spinner flowmeter device, fluid identification tools, borehole pressure and temperature measurements, along with natural gamma ray and casing collar locators. These logging tools should be combined into one tool string in order to provide simultaneous measurements, thus ensuring that all measurements are made under like conditions.
Objectives of Production Logging
There are objectives associated with production logging of which one primary function is to evaluate the flow of fluid both in the wellbore and outside the pipe. As in most logging applications, we measure certain physical properties and then use interpretation techniques to determine reservoir characteristics and extent of mechanical problems.
Objectives of production logs can be grouped into three broad classifications:
– To monitor reservoir performance efficiency throughout the life of a well.
– To define completion problems which are detrimental to maximum well performance.
– To gauge treatment effectiveness by injection/production profiles.
Figura. Production Logging Curves
Applications of Production Logging
There are many applications in both open hole and cased hole environments. Openhole applications can include locating loss of circulation zones and underground blowouts. Besides flow profiling in cased holes, other uses include locating top of cement, evaluating gravel pack quality, location of perforations, effectiveness of well treatments, and numerous others.
When performing injectivity test, production logs are used to determine where and what percentage of the injected fluid is displaced in the wellbore. This can help determine permeability comparisons, plugged perforations, and the locations of leaks in the casing/tubing and/or plugs and packers.
Production logging measurements usually consist of several types of logs, including temperature, fluid density, fluid capacitance, pressure, and spinner-flowmeter, along with standard casing collar locators and gamma ray logs. The type of flow regime and number of fluid phases will determine whether all of these are indeed necessary. These measurements are usually made in a single logging run for two primary reasons:
(1) to reduce rig time, and
(2) to make all measurements under the same wellbore conditions.
Multiple passes, both up and down, should be logged at different cable speeds to ensure correct spinner-flowmeter operations and eliminate any well instability effects.