Abstract
One of the challenges when performing hydraulic fracturing is treating reservoirs that are close to a water-bearing zone. Unfortunately, uncontrolled fracture height growth adversely affects many treatments and often increases the probability of water influx. This risk of fracture growth into the water zone eradicates the chances of applying hydraulic fracturing treatment to enhance well productivity, hence diminishing further production and more recoverable reserves. Therefore, involving hydraulic fracturing in such an environment is extremely challenging and demands proper design and execution. This paper includes a field example from the Eastern Desert, Egypt, in which an artificial barrier (referred to as a "settle frac") is established to limit height growth into the underlying water zone and confine the fracture geometry to the pay zone to increase fracture length in a tight oil reservoir, thereby increasing dimensionless fracture conductivity. The productive pay zone of the reservoir has a net pay thickness of 5 m and has very low permeability that ranges from 0.1 to 10 md. The proximity of the water zone to the hydrocarbon-producing zone varies from 5 to 10 m, with the absence of any stress barriers. The challenge in these conditions was to enclose the fracture height in the producing zone and prevent the fracture from propagating into the underlying water zone.
This paper describes the workflow followed in a pilot test of a dual hydraulic fracturing technique, from candidate selection to the post-treatment evaluation of the job. The work proved the importance of after-closure analysis (ACA) to obtain reservoir properties (i.e., initial reservoir pressure, Pi, and permeability, K) that match core analysis and formation tester (FT) data for a better understanding of the tight resources and optimizing hydraulic fracturing design. In addition, the work demonstrated the potency of the artificial barrier technique. This technique puts an artificial proppant barrier below the pay zone, close to the water-oil contact, formed by a low-viscosity fluid with high breaker loading and a proppant to create enough length and settled height to set up high resistance to fluid movement, thus limiting the vertical height growth of fractures. Using a smaller proppant size in the settle frac aids in reducing leakoff and in making the fracture longer inside the pay zone during the subsequent main treatment.
The results of the artificial barrier technique indicate a 50-fold increase in production with no water production with 3 months payback time of the investment. The results likewise reinforce the potency ofthe artificial barrier technique with a smaller proppant size. The application of this technique and understanding the reservoir flow properties (Pi, K), mechanical properties (σhmin), and the in-situ stress of the adjacent layers unlocked the reserve of 2 MMstb (P50) in tight oil sand, and it will be part of an optimized field development plan to enhance the estimated ultimate recovery (EUR) of the field and consequently net present value (NPV) for incremental investment in the field.
This paper shows the effect of employing the technique of placement of artificial barriers to curb fracture height growth. This novel technique facilitated the better development of this tight oil reservoir in the Eastern Desert fields.
