OVERVIEW

The popular perception is that acid jobs have a high failure rate. That is unfair, as success is very much site specific and largely dependent on practices employed. In any case, acidizing is often considered a hit-or-miss prospect. This reputation is understandable, if based on single-well results alone, rather than collective multi-well or fieldwide results, and if the factors leading up to and during the acid treatment are not considered.

In reality, there are a limited number of reasons, or controllable causes, for sandstone acidizing treatment failure. All can be avoided with proper treatment planning and execution. This is not to say that a success rate of 100% on a well-by-well basis is readily attainable. It may be possible in a particular field or with a limited selection of wells. ^[1] However, stimulation methods are not foolproof, and acidizing is no exception.

There are causes of stimulation treatment failure that cannot be controlled. These include unforeseen mechanical problems, especially downhole problems with the well and with tools, as well as problems with stimulation equipment on location. This cause of failure can be encountered more frequently in remote applications where equipment does not meet what should be required standards.

Another reason for failure that is part of the risk with stimulation, including acidizing, is the possibility that the treated well is a poor stimulation candidate. This is usually because the information needed to fully evaluate the well simply does not exist. However, some kind of stimulation treatment may still be attempted either as...