Increasing Productivity of Oil and Gas Wells: Key Methods

Introduction: The Inefficiency Problem in Oil Wells

Ali Daneshy's presentation, "Increasing Productivity of Oil and Gas Wells," examines the inefficiency of oil wells and potential solutions for increasing their overall maximum performance and profit potential. Drilling and maintaining oil wells is an incredibly expensive endeavor with high operating costs. Yet the natural flow found within a radial flow regime is inherently inefficient, which creates a pressing need for improved well productivity. The ability to increase productivity will ultimately raise the profit potential of oil wells. The presentation goes on to describe a number of alternative flow regimes and techniques that would help increase the overall productivity of oil wells.

Hydraulic Fracturing and Flow Regime Change

In many cases, oil production is inefficient. There are, however, ways that oil production can be increased — most notably through hydraulic fracturing. Certain elements can change the flow regime entirely. For example, a hydraulic fracture can shift oil flow from radial to linear. A fracture is most likely to change the flow regime when fracture permeability is much larger than formation permeability, though the actual fracture length also plays an important role.

A perforated borehole is one in which the boreholes enter from the side of a vertical flow. In this configuration, the pad volume is what causes the fracture in the first place, creating a situation in which the well can accept proppant. This then allows the proppant concentration to increase within the subsequent slurry. As Daneshy notes, the "proppant gets closer to the fracture tip as the pad leaks into the formation" (Daneshy 6). This decreases the width of the pad as the volume of the slurry increases. The final step in this process is the displacement of the proppant from the borehole into the fracture, accomplished with the assistance of clean fluids. This process proves effective in increasing the overall productivity of oil wells.

The presentation also addresses the challenges of producing oil from shales, also known as ultra-low-permeability reservoirs. In these formations, permeability is so low that production from the well does not always cover the costs of construction and maintenance — a clear illustration of how oil production can be deeply inefficient. In such cases, even hydraulic fracturing alone cannot increase overall well productivity sufficiently.

Shale Reservoirs and Horizontal Drilling

The most effective approach for these reservoirs is to drill horizontal wells, after which hydraulic fracturing can be conducted at multiple points along the structure of the horizontal well over time. Horizontal wells offer several advantages. First, they increase the actual contact length "between the wellbore and formation," which enhances the effectiveness of hydraulic fracturing and enables more efficient well measures (Daneshy 8). The ability to fracture at multiple locations creates a greater contact area, thereby increasing the overall efficiency of the well.

Fracturing can even take place within cased and cemented horizontal wells. The well must be perforated at the point closest to its "toe" and fractured to improve efficiency. Before opening another fracture in the horizontal well, it is important to set a bridge plug between the two fracture points in order to isolate the previous fracture. This procedure must be repeated as many times as the desired number of fractures requires.