Some Solutions to Necessary, but Risky, Open Hole Well Development

Boreholes in fractured rock are often drilled for two reasons, water supply or contamination assessment and remediation. Both uses benefit from development of the well. Well development of a cased hole with a screen and filter pack is easy. Development of an open uncased hole in fractured rock is much more problematic. In an open hole, the usual development methods can collapse the hole, trap tools in the hole, or lead to other extremely costly consequences. However if the transmissivity distribution is an important parameter to the situation, and it usually is, the transmissivity of the formation cannot be measured with the fractures plugged with drill cuttings. Casing the hole is not an option if access to the entire formation is needed. This paper describes some of the relative merits of several development techniques in open holes. Some measurements are provided showing the effect of insufficient well development in open holes. The practical limitations of some common methods are calculated. The production of large amounts of contaminated water can be costly. A new technique using a flexible liner is added to the list of development methods. Transmissivity changes during the development process should be measured to help determine when the development procedure is sufficient to the purpose of the borehole. Several such measurement methods are described. Examples are provided of the results of development in sandstone and limestone formations using flexible liners.