FRACTURE WIDTH AND EMBEDMENT TESTING IN SOFT RESERVOIR SANDSTONE

A new computer-controlled laboratory technique has been developed to m easure propped fracture width and embedment in weakly consolidated cor es or unconsolidated sands under simulated downhole conditions. Previo usly, laboratory studies on cores had determined embedment in hard roc ks where embedment was normally limited to 50% of the proppant grain d iameter. Several studies also indicated the importance of embedment wi th one monolayer or less of proppant coverage. The effects of water sa turation and fracture-fluid filtrate on formation softness and embedme nt have not been previously published. Consequently, the objectives of the current paper are to extend previous research results to include soft, weakly consolidated cores and unconsolidated sands with multiple proppant layers. The influence of water saturation and dynamic fluid leakoff on embedment are also shown to be important. The current inves tigations indicate that embedment becomes a problem when the Brinell h ardness (BH) of the formation is less than about 20 kg/mm(2) or when t he static Young's modulus of formations cores is less than about 2 mil lion psi (13 GPa). Embedment has been determined for cores with static Young's moduli between 0.1 and 1.4 million psi (0.7 to 9.6 GPa). In s oft and wet sandstone, embedment can reduce fracture width up to 60% o r more for proppant concentrations of 2 Ibm/ft(2). For unconsolidated sands, embedment is influenced by fracturing-fluid type, water saturat ion, and downhole conditions. Cyclic loading conditions associated wit h well shut-ins also increase embedment in unconsolidated sands. This paper reviews and discusses test data on formation cores from south Te xas, New Mexico, the North Sea, and the Gulf of Mexico. Most of the co mmercial fracture-design programs neglect embedment problems in calcul ating fracture width, while other fracture simulators contain allowanc es for embedment.