The Possible Detrimental Effect Of Clays In Completing Wells For Optimum Production Or Injection
Authors: Carney Leroy L. , Taylor Ray 
Published: December 2007

Because of clays, use of liquids for drilling, cementing, completing and perforating wells for the purpose of production perforating wells for the purpose of production or injection can be considered a necessary evil.

The characteristics of a fluid should be carefully selected so that the permeability of a given formation will not be sacrificed. For example, the poor quality of many wells can be traced to undesirable characteristics of the completion fluid. There is less chance of sacrificing permeability, and, better results, when more information is used in planning fluid utilization. planning fluid utilization. The production branch of the petroleum industry is interested in the swelling properties of clays because these minerals properties of clays because these minerals occur widely in oil producing rocks. With their large surface areas, the clays are capable of significantly affecting the flow of oil to producing wells.

The rock wettability is important when considering flowability of fluids through small capillaries, in addition to the detrimental effect of clays on fluid flow through formations which is well documented.

The paper presents preliminary data on flowability of various fluids through rock having different wettability characteristics. If the right choice of a fluid is made, fluid leak-off (filtrate) can be contained to shallow depths, or, very deep invasion can occur if the wrong choice is made.

This fact, coupled with the possible detrimental effects of clays when contacted by fluids, makes the selection of a fluid for performance a complicated procedure. performance a complicated procedure

Introduction

It is unfortunate that liquids must be used to drill and complete wells. Ideally, we would prefer to use pure air to total depth because this would eliminate problems associated with changes of a formation due to liquid invasion. Any liquid may inflict some damage to the permeability of a formation when it comes in contact with the solids and the conant fluid found within this formation. Since liquid contact, with pay and injection zones, occurs during drilling, coring, cementing, completion, workover, and injection operation, consideration of formation damage to permeability should be exercised in practicing each of these operations. practicing each of these operations. Minimum damage should be the prime criteria in the design of any program utilizing fluids for any of these operations. The selection and design of fluids that provide maximum formation protection, yet provide maximum formation protection, yet fulfill their primary intended purposes, is not simple. The choice is usually based on engineering functionality. However, some compromise may be made in order, to optimize a system to cover the important aspects of formation damage.

The presence of clay minerals is probably the most important, and complex aspect relating to formation damage. However, recent tests show that damage to flowability through rock can also occur in formation which are void of clays. More importantly, tests imply that an improper choice of fluid can cause much deeper damage than skin damage. When formation damage is deep, any remedial measures become more difficult to correct; even when using the most current technology.

In this paper, the potential effect of different fluids on formation damage is discussed.