3D Geomechanical Modeling for an Extra Deep Fractured Carbonate Reservoir, Northwest China

Abstract

The development well drilling for the deep carbonate reservoir in Shunbei field, located in Tarim Baisn in Northwest of China, has been challenging because of the great depth, complex lithology, highly fractured reservoirs and the stress condition of the field. Although vertical wells could mostly be drilled to over 7,000 m deep by continuous reaming, deviated well drilling turned out to be extremely challenging. These wells are associated with frequent hole instability related issues such as stuck pipe and pack off, which results in sidetracks. To help understand the different drilling behaviors in different parts of the Shunbei field, a pilot area was selected to construct a 3D geomechanical model to understand the lateral variations in stress and rock properties by integrating the spatial structural and lithology changes. A 3D geomechanical model is built using the well-based models as foundation and integrating the surface seismic interpreted surfaces, attributes and velocity volumes. Based on detailed well-centric geomechanical modeling, an understanding of the three principal stresses, pore pressure and rock mechanical properties and parameters of the formations was previously developed at the offset wells locations in Shunbei field. Rock mechanical properties, pore pressure and stresses were populated in 3D space using inverted seismic volumes and relationships developed in the well-centric models, honoring the 3D static geological and structural models. 3D geomechanical modeling is an effective method to capture the lateral variations away from the offset wells and helps to diagnose and understand the drilling problem in the complex deep carbonate reservoir.

Optimization and Performance Evaluation of an Atomized Acid System for the Expansion of Carbonate Gas Injection

“…As shown in Figure 1, due to the special structure of fractured-vuggy reservoirs, when conventional acid is used for matrix acidification, under the action of gravity, a large amount of acid is stored in the lower space of the karst cave and it is difficult to form continuous and effective acid etch wormholes at the high parts of the karst cave for oil and gas seepage. However, atomized acid is uniformly distributed in the form of a fog, which is less affected by gravity and can be uniformly dispersed into the cave space with a wider spread range, which is more conducive to etching and starting underdeveloped gas drive channels and the extension of acid etched wormholes, increasing the probability of gas communication with new reservoirs [17][18][19]. In addition, compared with conventional acid acidification, atomized acid also has the following advantages: 1 the atomized acid filtration loss is smaller and the acid consumption is much less than conventional acid; 2 it is easier to form wormhole dissolution by atomizing acid acidification; 3 the reaction rate of atomized acid rock is basically not affected by the flow rate; 4 atomized acid can still play a normal role under high temperature conditions; and 5 when atomized acid acidification is used for acid injection, the construction friction is small.…”