Selelctive Fluid Placement Improves Stimulation Results
Authors: Ripley H.E. , Young F.T. 
Published: March 2010

Perforation isolation for selective treating and for production testing is necessary to insum total zone treatment or evaluation. Two series of downhole tools are available to the industry so that one-foot, or greater, portions of the wellbore can he isolated.

The previous method of treating the total interval at one lime, where the treating fluid takes the path of least resistance, could leave some perforations untreated. The tools can be used for washing per/orations wish acids or surfactants, sand consolidation treatments, using 'I single fluid or several fluids, andfor other treating purposes. Downhole recorders will provide positive indication of segregation or communication. The integral tool systems provide ease of operation and positive operation, resulting in minimum cost to the operator.

A retrievable fluid control valve is discussed. This valve allows an operator to limit the hydrostatic pressure exerted on a formation, reducing the risk of overtreating low-fluid-level wells with expensive chemicals or loading the zone with a large volume of flush fluid. Field experience using these assemblies is outlined and several basic procedures are discussed.

Introduction

The uncertainty that a wireline perforating charge will create a channel which will permit fluid to communicate between the well bore and the formation is well documented in the literature:(1,2,3). Even though an interval has been perforated over its entire vertical height, all of the perforations may not be open, or they may not have penetrated the damaged zone around the well bore. The effect on productivity or injectivity will be similar to a partial zone completion.(3)

It is not the purpose of this paper to analyze the weakness in perforating charges and perforating techniques, but rather to discuss several specialized tools which, either used separately or in combination, will help overcome the problem of non-effective perforations.

Perforations that have become plugged over a period of time with scale, paraffin or other debris cannot function as flow channels between the well bore and the formation. Solvents are normally available which will react with the plugging material. The problem in designing a cleanout or stimulation treatment is how to ensure that the plugging material in each perforation will be contacted with the treating solution.

For sand consolidation treatments to be successful, it is vital that the consolidating chemicals are injected into every perforation.(4) One of the problems in designing a sand consolidation treatment is how to ensure that the sand grains behind each perforation will receive their allotment of chemicals.

Every foot of a perforated interval can now be individually treated, during stimulation or sand consolidation treatments, with a minimum of effort and expense.

Current completion techniques, using limited entry(3) or pseudo-limited entry(6), normally will give fair assurance that all perforations will be treated. For older wells that were indiscriminately perforated with many shots per foot, or for any well where the number of perforations make the application of pseudo-limited entry techniques doubtful, some other form of selectively treating should be considered.