Doctrines vs. Realities in Reservoir Engineering

The appreciation of empirical realities permits the improvement of commercial depletion planning and enables a greater number of projects. The concepts articulated here are applicable in almost all heavy-oil reservoirs and may be applicable also for lighter oils that possess oil chemistry typical of heavier oils (e.g., high acid content). This paper reviews the evidence for and against three doctrines in current use to develop depletion plans: (1) optimal recovery is obtained using a voidage-replacement ratio (VRR) of unity, (2) the Buckley-Leverett (BL) formulation (phase slippage) applies uniformly to heavier oils, and (3) viscous fingering dominates unstable multiphase flows.

VRR=1

  • Doctrine: Optimal Waterflood Response Occurs With VRR=1
  • Reality: Periods of VRR<1 Increase Oil Recovery

Though initially viewed with some suspicion, waterflooding has demonstrated multifold greater recovery than primary depletion for many reservoirs. It is, by far, the most important oil-recovery process. One visualization of the process is that of a leaky, deformable water piston displacing a fraction of the oil to the production wells. Maximum recovery occurs when the voidage created by the produced fluids (oil plus water) at reservoir conditions (pressure and temperature) is replaced fully by an equal volume of the injected water also at reservoir conditions (i.e., the waterflood VRR=1). In this way, reservoir pressure is maintained. The waterflood initial production is pure oil until water breakthrough. Subsequently, water is produced along with the oil, resulting in an increasing water/oil ratio (WOR). This simple visualization is intuitively attractive and has dominated the thinking of the industry.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 185633, “Doctrines and Realities in Reservoir Engineering,” by Euthymios Vittoratos, Petroprognostica, and Anthony Kovscek, SPE, Stanford University, prepared for the 2017 SPE Western Regional Meeting, Bakersfield, California, USA, 23–27 April. The paper has not been peer reviewed.
...
This article is reserved for SPE members and JPT subscribers.
If you would like to continue reading,
please Sign In, JOIN SPE or Subscribe to JPT

Doctrines vs. Realities in Reservoir Engineering

01 March 2018

Volume: 70 | Issue: 3

STAY CONNECTED

Don't miss out on the latest technology delivered to your email weekly.  Sign up for the JPT newsletter.  If you are not logged in, you will receive a confirmation email that you will need to click on to confirm you want to receive the newsletter.