MECHANISM OF SAND PRODUCTION IN A HYDROCARBON RESERVOIR

Abstract

This thesis uniquely confers a tempting insight of ‘Mechanism of Sand Production in a Hydrocarbon Reservoir’. This study deals with the topic in three aspects – theories governing sand production, prediction and estimation of sand production, and sand production control techniques. The area of study is Tapti-Daman block. Tapti-Daman block is present in the Cambay Gulf area, which forms the north-eastern part of Bombay Offshore Basin. The problems encountered are: 1. The sandstone reservoirs which are unconsolidated and have a permeability of 0.5 to 8 D are more prone to it. 2. This sand production usually occurs during later part of drilling when reservoir pressure falls and during the start. Solid (sand) production will initiate when the critical collapse pressure exceeds the pore pressure. In porous rock, pore fluid carries part of the load, so pore pressure is the failure controlling parameter. In this study, the fundamental data used were: stress (𝜎𝐻, 𝜎ℎ, 𝜎𝑉), angle of internal friction (𝛷), cohesion (C), depth (h), Poisson’s ration (𝑣), initial pore pressure. These fundamental data were further used to derive the other required data like material constant, depleted pore pressure, well collapse pressure etc. The prediction of sand production can be done by two failure criteria, Mohr-Coulomb Criteria, and Mogi-Coulomb Criteria. The former one estimates higher value of critical collapse pressure as it ignores the effect of intermediate principal stress. Mohr-Coulomb Criterion shows sand production in all the cases, and at all depth, which contradicts the field observations. Whereas Mogi-Coulomb Criterion shows different amount sand production at different depth in different cases, which coincides with the field observations. This implies that Mogi-Coulomb Criterion is suitable to be used in this case. There are three approximate zones of sand production: a) 350 m – 550 m, b) 1000 m -1400 m, and c) 1900 m – 2200 m. In zone ‘a’, sanding starts at 0% depletion, in zone ‘b’ it starts at 10% depletion and in zone ‘c’ it starts at 60% depletion. Looking at the Cohesion vs. Depth graph, we see that cohesion is very less in the zones of sand production, and it is lesser in the zone of more sand production. From this, we can deduce that the sand production is happening mainly due to low cohesion (loosely bound particles). Grain size distribution is uniform. The grains in a zone are well sorted. Therefore, based on the grain size distribution and grain sorting, following sand control techniques can be used: a) Stand Alone Screen b) Gravel Packing