Example 2: Well Completion Optimisation

The goal of this exercise is to present a simplification of the well completion optimisation study. The study has been performed using WellWhiz.

In a typical stimulation study sensitivities to the variation of several parameters can be studied. This includes but is not limited to:

• Number of fractures per well
• Type of fracture (acid vs proppant)when applicable
• Fracture dimensions (length, width and height)
• Type of proppant
• Optimum placement of the wells in the reservoir given that stimulation changes reservoir recovery
• Secondary recovery methods

The following geology layer model is to be used for the example:

• Initial reservoir pressure: 4,750 psi
• Reservoir temperature: 180°F
• OIP: 28.50 Million STB
• Reservoir top: 9,382ft
• Formation thickness: 264ft
• Layers in model: 7
• Horizontal permeability: 1mD
• Vertical permeability: 0.3mD
• Porosity: 40%

The WellWhiz grid is presented below:

The following PVT characterizes the reservoir fluid:

Default correlations are used to model the relative permeability properties of the fluid system.

Sensitivity to stimulation type.

The first step is to assess the type of stimulation that should be used (if applicable). Acid treatments provide very high fracture conductivity, although the fracture extension is limited (normally short fractures Ca. 50ft half length). However, with infinite conductivity, non-Darcy effects are negligible.

To asses which type of stimulation would yield better productivity, two different stimulation scenarios were run using WellWhiz. The two different scenarios represented typical propped / acidized fracture dimensions and conductivities. The figure below presents a comparision between the oil rates for the two cases mentioned.

The bottom hole flowing pressure during the simulations is set as 4,000 psi.

It is obvious from the simulation results that the propped fracture yields better oil productivity.

Sensitivity to fracture spacing.

The simplification presented below consists of the study of sensitivity to fracture spacing along a horizontal well. For example, it is assumed that only one proppant is available and that, from previous studies it is know that the reservoir beneficates from large fracture placement.

From the relevant fracture design, the following dimensions are the maximum achievable given operational constraints.

• Fracture half length: 500ft
• Fracture width: 0.34 inches - Ca 4 Lb/ft²

The three scenarios considered include the simulation with 2, 4 and 6 fractures equally spaced along the horizontal section of the well.

Non-Darcy flow effects are to be considered in the simulation. β is considered constant (α=81,999, n₁=0, n₂=0).

Well completion performance comparison