Gas Coning Control for Smart Wells

Abstract

A strong increase in gas influx due to gas coning and the resulting bean-back because of Gas to Oil Ratio (GOR) constraints can severely limit oil production and reservoir drive energy. The purpose of this paper is to demonstrate that oil production after a gas breakthrough can be optimized by means of an inflow control strategy that takes the effects of 'natural gas lift' and production choking into account. Within the research framework of the "Integrated System Approach Petroleum Production" (ISAPP) knowledge center of TNO, TU Delft and Shell, it has been shown that this optimization can be achieved by controlling the location and amount of gas influx in a horizontal smart well. In order to show a proof of principle we have implemented a PID feedback controller, which controls the gas fraction in a well by changing its Inflow Control Valve (ICV) settings, on a test case in a dynamic reservoir simulator. We introduce a three step strategy for production optimization: firstly we model how the controlled production rate after breakthrough depends on the gas fraction; secondly we will determine the optimal gas fraction; thirdly we will consider the capability of a PID controller to produce at this optimal gas fraction. Simulation experiments show that a PID controller is an effective means to prevent a full gas breakthrough and, moreover, can be used to increase the produced oil rate by tuning ICV settings to an optimal gas fraction. These experiments also demonstrate the benefits of using downhole ICV control in comparison to wellhead control. In current operations ICVs are mostly used to completely shut down well segments that experience gas coning. We show that by keeping these ICVs open in a controlled way the, otherwise undesirable, phenomenon of gas coning can be used to optimize oil production. Introduction: Gas Coning Gas coning is a phenomenon where the gas-oil-contact (GOC) of a reservoir slowly moves towards a well as a result of oil drawdown. In case of horizontal or deviated wells this is often a zonal phenomenon, which occurs at a limited amount of perforations only, and is referred to as 'cresting' (Figure 1). At a certain moment in the production life of a gas coning well the gas-oil-contact will reach the well and a gas breakthrough will occur. Upon breakthrough the well will experience a high gas influx. Largely for three reasons this is an undesired phenomenon. Firstly because the gas phase may start to dominate production, which will deem the well to be uneconomical. Secondly, the influx of gas may damage topside equipment that is not designed to process large quantities of this phase. Thirdly, after breakthrough the gas cap of the oil reservoir will be depleted fast, taking away its drive energy.

Real Time Optimization of a Natural Gas Lift System with a Differential Evaluation Method

“…Although this part can be useful for controlling the fast changes, it may cause the system to become unstable. Designing these controller parameters must be done in a such a manner that the controller gives a high performance and the system remains stable (Leemhuis et al, 2007). A traditional method called Ziegler-Nichols can be used to design the controller parameters (Astrom and Hagglund, 2004), but in this work the authors have designed these parameters using a trial and error procedure.…”

“…After that the amount of GOR will be high enough and well can flow naturally. This is the case when thin oil rims are produced by horizontal wells (Betancourt et al, 2002;Leemhuis et al, 2007). The productivity index of gas and oil zones, the pressure of gas and oil zones, the composition of gas and oil zones, and the pressure losses through inflow valves and piping systems are all the factors that affect the operational conditions of a natural gas lift system.…”

Effectively optimizing production of horizontal wells in homogeneous oil reservoirs

“…Owing to the fact that cresting is a natural phenomenon which will occur at some point in the production life of a horizontal well despite producing at a water and gas-free oil rate 'critical rate' (Leemhuis et al, 2007), there is a need to determine an optimum well geometry for better oil recovery in reservoirs with cresting problems. Previous researchers have investigated the use of horizontal wells in reducing cresting effects but have only considered the effect of varying the lateral lengths and measured depths (MD) of inclined or deviated wells without considering the effect of the steepness of such wells on its performance such as in the works of Balazs et al, 2009.…”