Geothermal Energy in Caspian Region: Study of Heat Extraction Methods from Deep Wells

Abstract Geothermal energy currently occupies an insignificant role in the renewable energy balance. This is explained by its low heat flow rate and the significant investments associated with heat mining. However, the geothermal heat flow is continuous and non-interruptible and occurs everywhere in the lithosphere. Existing oil and gas fields’ subsurface and surface infrastructure and expertise can significantly decrease capital expenditures for geothermal heat extraction. Taking this idea as a basis, the study of geothermal heat production from existing oil and gas fields of the pre-Caspian region of Kazakhstan was performed. Since this work is one of the first attempts to estimate the geothermal heat potential of the existing oil and gas industry infrastructure in Kazakhstan, the study consists of two big parts. First part is the detailed theoretical review of the geothermal heat extraction methods which may be potentially applied in Kazakhstan. Special attention in the literature review section was given to enhanced geothermal systems and closed loop systems, because they have many technologies in common with the oil and gas industry (completion concepts, hydraulic fracturing etc.). Second part is the quantitative estimation of the geothermal potential based on twenty oil fields, with several wells in each field as trial sites. Quantitative estimation considers pragmatic and optimistic scenario of future investments. The study showed that even in the pragmatic scenario in which the water-producing wells are turned into hydrothermal producers, the recoverable effective heat reaches 420 TJ in total for all wells in the selected fields. However, the demand for the geothermal heating of the industrial and household objects near the selected fields was estimated to be three times higher. Thus, a more proactive geothermal strategy was considered. This strategy yields ~9800 TJ of recoverable effective heat, which covers the demand and provides excess for the growth. Based on the reservoir properties and economic perspective estimations, it was defined that enhanced geothermal systems and closed loop systems will be less abundant in the given region in a short term. However, with development of the geothermal technologies and increase of investments, these systems may have increased importance. On the other hand, direct hydrothermal producers and well doublets (injector connected to producer through the permeable reservoir), most probably, will be a prevailing method of the geothermal heat mining in the pre-Caspian region of Kazakhstan in the short and medium terms.