Flood Management: Solving Conformance or Sweep Efficiency Problems—Part 2: Connecting Problems to Solutions

Abstract

_ In Part 1 we discussed the process wheel and the first two elements of that wheel, namely candidate selection and problem clarification. In Part 2 we will focus on generating a connection between the problem types as outlined in the conformance problem matrix and various methods of trying to solve these problems. In this section we continue to utilize the conformance problem matrix outlined in Part 1 and incorporate various overlays on this matrix to describe how elements of the conformance solution continuum and the subsection of the continuum, i.e., existing wellbore interventions, can be used to show how these solutions can be effectively applied. Defining the Problem Matrix Prior effort to classify conformance engineering problems have used a linear view of grading problems from easiest to most difficult to control. Probably the most quoted document in this effort is by Seright et al., SPE 84966. Although I don’t disagree with their ranking process, it really doesn’t help us to focus on the most appropriate solution. A different way of classifying conformance problems was developed, briefly described, and presented in Part 1. The conformance problem matrix (Fig. 1) allows us to classify conformance problems based on two primary problem characteristics: the dominant problem flow path (i.e., a VSC [void-space conduit] or permeable rock) and the location of prominent flow control (i.e., near the wellbore or deeper in the reservoir). Although some problems can contain multiple characteristics, the key is to define the most dominant characteristic so it can be solved first. Populating the Problem Matrix Populating the matrix with every problem type that we face within the industry would create a very cluttered chart. One thing to recognize is that the wellbore is a VSC that we created to connect us to the reservoir. Anytime we lose control of how fluid enters the wellbore from the reservoir, we have a VSC. Thus, we start by reviewing the more common problems associated with losing control of the wellbore such as casing leaks, packer leaks or plugs, mis-perforated intervals, cement channels, perforated wrong interval, etc. These problems all fall in the upper left quadrant. Since they are strictly void space or conduit flow, they are controlled totally at the wellbore. The next example helps us understand the importance of geologic controls and understanding. If we have a watered-out layer with no crossflow between layers, this problem falls in the upper right quadrant, since the flow problem is dominated by permeable flow, but due to no crossflow between layers, all the control exists at the wellbore. We then move to the more complex problem of a watered out layer, but one with extensive crossflow between layers. This problem would fall in the lower right quadrant as the flow problem is permeability related, but since there is extensive crossflow, there is really limited or no control at the wellbore. These last two problems exist as a continuous grade from the upper right quadrant to the lower right quadrant, depending on the level of crossflow between layers.