New Insights into Water Control - A Review of the State of the Art

Abstract

Abstract It could be argued today that oil companies would be better described as water companies. Total worldwide oil production averages some 75 million barrels per day (BOPD) and, while estimates vary, this is associated with the production of 300–400 million barrels of water per day (BWPD). These values of approximately 5–6 barrels of water for every barrel of oil are quite conservative. In the United States, where many fields are depleted, the ratio of water-to-oil production is closer to 9-to-1. In some areas around the world, fields remain on production when the ratio is as high as 50-to-1. Water production is always a harbinger of problems in an oil well. It can cause scaling problems in susceptible wells, induce fines migration or sandface failure, increase corrosion of tubulars, and kill wells by hydrostatic loading, amongst other things. Thus, while water production is an inevitable consequence of oil production, it is usually desirable to defer its onset, or its rise, for as long as possible. Numerous strategies, both mechanical and chemical, have been employed over the years in attempts to achieve this. Simple shut-off techniques, using cement, mechanical plugs and cross-linked gels have been widely used. More exotic concepts, like relative permeability modification (RPM), have also been applied with varying degrees of success. This paper reviews the traditional techniques and proposes some new methodologies and technologies that can be used in the design of RPM treatments, in particular. New insights offered in this paper have been gained from the design and analysis of various experimental treatments around the world. The paper includes several of these, as case histories, to support the concepts and conclusions. Introduction Water cuts in oil producing wells are increasing as time passes and oil fields become mature. The source of the water is either formation water or injected water used for reservoir pressure maintenance purposes. In addition, heterogeneities encountered in reservoirs rocks can cause water channeling through higher permeability streaks/hairline fractures and/or near wellbore water coning at early times in the well's productive life, usually due to limited reservoir thickness or excessive pressure drawdowns. Whatever the scenario, the cause is always associated with a higher mobility of water relative to oil. Usually, the lower the oil API gravity the greater the chance of water production, since low gravity oils are typically much more viscous and, hence, have lower mobility. However, mobility is not the only factor. Additional wettability effects caused by heavy oil deposition, produced by pressure and temperature cycles in the near wellbore area, compound the problem. Apart from mechanical tools, and the traditional cement and inorganic gel squeezes frequently used to isolate watered out zones (water shut-off and not water control treatments), several types of gellant systems have been used with some degree of success to control water production. There are three main types of chemical gel type treatments:Permeability blockers or gellantsDisproportionate Permeability Reducers (DPR) and or Selective Permeability Blockers (SPB)Relative Permeability Modifiers (RPM) It appears, from the literature, that there is some confusion by authors on the intrinsic differences between them and how they should be injected/placed in the formation. Actually, we believe that this is the main cause for poor historical results. A few examples are included under the jobs review section. Several models have been used in an attempt to explain the governing mechanism for these different materials to understand how they work and optimize design.