An Integration Approach for Evaluating Well Deliverability in Ultra Deep Sands

Abstract

Deep and ultra deep low-permeability reservoirs are widely distributed in the South China Sea, such as HuiZhou 19-1, 26-3, 9-2 oil field and PanYu 34 gas field. These ultra deep reservoirs generally performed as deep burial depth, low porosity, low permeability, which lead to difficulty in evaluating well deliverability. DST is a fast and valid well test method for deep sands. The DST showed that layer M-31 of well HuiZhou 19-1 had a relatively higher productivity. However, the layer M-32 with the same perforated thickness only produced about 1.6 m3 each day. While the layer M-32 and M-31 has a vertical distance of about 25m and similar porosity and permeability. In order to evaluate well deliverability of layer M-32 and M-31, effect of mineral components and pore structure on DST was analyzed. 13 groups of start-up pressure and 13 groups of stress-sensitive experiments were also carried out. This work indicated kaolin clay in the soil minerals of layer M-32 damaged the formation and had an important impact on well deliverability from DST. In addition, layer M-32 offered an relatively high start-up pressure gradient, which reached the magnetite of 10-1 to 10-2. When effective stress was more than 15 MPa, the porous media would begin to deform seriously. The integrated approach indicated optimized production of the layer M-31 and layer M-32 of well are 2413.1 m 3 /d and 86.39 m 3 /d respectively. Numerical simulation also showed that enlarging producing pressure drop, hydraulic fracturing and horizontal wells can further improve well deliverability of deep and ultra deep low-permeability reservoirs. The study also suggested effect of kaolin clay and start-up pressure gradient on DST should be considered correctly.Common problem existed in production of low permeability reservoir:Reservoir pore is small, surface area is large, permeability is low Flow characteristics do not follow Darcy's law, and the starting pressure gradient is existed.Elastic energy is small, the exploitation pressure and production decline fast with using of natural energy recovery The capacity of Oil production and water absorption is very low; the effect of injecting water in oil well is slow. Oil production after water breakthrough decrease significantly. Along the crack direction the water channeling and flooding of oil well in fractured low permeability sandstone is serious.The effect of clay minerals in rock on the production of test M-31 layer is the major reservoirs of Huizhou 19-1 oil field. The effective thickness of the layer is17.6 m, the porosity of well logging is11.6% and permeability is 19.4mD; the effective permeability of drilling test is 157mD, underground oil density is 0.727 g/cm3, underground oil viscosity is only 0.73mPa.s. The reservoir properties and crude oil properties is good, therefore the layer have a higher capacity 3,12 .