Evaluation of Hydrofracture Technology in Selected Geological Formations in Ghana

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The Community Water and Sanitation Agency, has been charged with the responsibility for the provision of sustainable water and sanitation facilities and the setting up of management structures for operation and maintenance of these amenities in the rural communities and small towns. The Agency is committed to utilizing Government and donor funds as economically as possible to supply all communities with potable water. In view of this the CWSA is committed to use the best available technological options to achieve its aim. Appropriate scientific methods of siting for boreholes and state-of-the-art methods of drilling are employed in order to minimize the number of dry wells and to reduce the overall cost of drilling. In certain crystalline geological terrains in Ghana such as the granite and other metamorphosed rocks, it is difficult to obtain borehole yields required to declare them as successful (13.51pm by CWSA standard) boreholes, although there will be indication of fractures from the drilling logs. Experience has shown that apart from the naturally poorly developed or low yielding fracture systems, some degree of plugging of fractures by fine materials take place during most drilling operations. To realize the full potential of a fracture system, these fines must be removed and the tight or poorly developed fractures opened up to facilitate the flow of water into the borehole. Hydrofracturing has been one of the standard methods of achieving this. Hydrofracture is a well development/rehabilitation method used to increase the yield of low-production boreholes completed in rocks where the fracture/joint systems have been blocked or are so poorly developed or so tight that little or no water can move through them. Since 1995 about three hundred and nineteen (319) boreholes have been hydrofractured in various geological formations such as granite, schist, phyllite, quartzite, sandstone and shale. Two hundred and thirty three (233) out of this number have been successful in Central, Volta, Eastern and Greater Accra Regions in Ghana to augment the existing Evaluation of Hydrofracture Technology in Selected Geological Formations in Ghana twelve thousand (12,000) successful boreholes (CWSA Data Coverage, 2001). Indeed, “Little drops of water make a mighty ocean”. The results so far indicate that the Hydrofracture technique has been very successful in improving the yields in all the terrains except in the shales and siltstone formations. Boreholes in granite, phyllite, sandstone and schist showed improvement of over 200 % in specific capacity. The cost benefit analysis shows that there was a saving of 20% when a dry borehole is hydrofractured instead of drilling a replacement. On the social aspect, boreholes could be drilled closer to the community and this creates a favorable condition for future maintenance of the system, which is of very high interest to CWSA Almost all the hydrofractured boreholes are performing satisfactorily and the beneficiary communities have no complaints whatsoever. Considering the advances made in the hydrofracture technology, the high success rate in granites, reduction in cost of hydrofracturing a marginal or dry borehole against drilling a replacement well and the higher uncertainty of the result when drilling a new well in crystalline rocks, it is recommended that a policy should be established to cap all dry and marginal wells in the granitic formation in Ghana for hydrofracturing, because, “a bird in hand is better than two in the bush.”
A thesis submitted to the College of Engineering in partial fulfilment of the requirements for the degree of Master of Science, 2003