Development of Simple Rock Scratching Cell for Unconfined Compressive Strength Estimation

The mechanical properties of rocks are of high importance for oil and gas wells drilling, production, and future development. Rock mechanical properties are needed for maintaining borehole stability during oil and gas wells drilling and completion stages. Additionally, these properties are needed to select the optimum production rate especially in soft formations to avoid many problems such as sand production. The evaluation of such properties requires a sufficient number of standard core samples and sophisticated testing equipment. When there is a lack for sufficient core samples or testing equipment, rock mechanical properties can be predicted using correlations or simple indirect tests such as scratching or indentation. In this study, a simple and cheap rock scratching cell was developed and manufactured in-house (college workshop). The validity of this cell was tested using strength and scratching data generated from testing of fourteen rock samples covering rocks strength range. The measured unconfined compressive strength (UCS) and scratching resistance strength (SRS) data were located in the same region of similar laboratory data obtained by other researchers using very sophisticated and expensive testing equipment that are not available in the market. Furthermore, using the rock scratching cell developed in this study, it is found possible to perform scratching tests using small rock fragments. A correlation between SRS and UCS was developed based on laboratory measurements performed in this study in conjunction with published similar data. Therefore the developed rock scratching cell provides an excellent mean for predicting rock unconfined compressive strength using scratching test results.