Formation Damage Means of Prevention Using Workover Completion Fluids

Sedimentary formations are the usual target for oil and gas exploration. Of the many classifications of these zones, carbonate and elastic deposits most often bear hydrocarbons in commercial quantities. Clastic formations are composed of broken and fragmented pieces of older existing rocks. Sands or sandstones can be classified as elastics. They result from erosion and weathering of land masses. The eroded particles are transported by various means to an area of deposition where they are laid down in somewhat orderly strata. Carbonate rocks result from the precipitation of minerals held within an aquatic environment. Carbonates are formed of varying concentrations of calcium and magnesium carbonates. Most texts represent sedimentary rocks as orderly strata arranged in uniform distribution. It is very important to remember these zones are actually composed of numerous individual grains of fundamental makeup materials. The size, shape and homogeneity of the matrix greatly contribute to a formation's ability to store and later transmit hydrocarbons. For the purpose of this discussion, any change in the potential for production caused by foreign fluid exposure will be classified as formation damage. There are four primary formation damaging mechanisms commonly recognized in most sedimentary hydrocarbon bearing zones. These mechanisms are (1) the hydration and swelling of formation clays, (2) the invasion and/or migration of solids into and within the formation, (3) the formation of water blocks, and (4) the formation of emulsion blocks. The damage resulting from any one of these sources can be seriously detrimental to well productivity as well as extremely long lasting. The prevention of these types of damage is much less involved than rectification after damage has occurred.