Cold Production And. Enhanced Oil Recovery
Authors: Dusseault Maurice 
Published: March 2010

Introduction

Economical heavy oil production is possible by allowing formation sand to be produced along with fluid. Cold production has potential to increase subsequent enhanced oil recovery (EOR) efficiency, operating new technological possibilities for continuedeconomical oil production from these reservoirs. Heavy oil (10–15 ºAPI) in cohesionless sandstones (&gt;30% porosity) can be exploited by permitting sand to enter the wellhole along with fluids. Information from Lloydminster and North Primrose areas is given in Table 1. To achieve sustained production, sand production must be encouraged through use of closely spaced high-energy perforations and through application or work over strategies that re-initiate sand production if it has stopped. Sand exclusion is disastrous; free sand flow is vital production mechanism, as yet incompletely understood(1). Blocking it by gravel packs or screens simply reduces the oil now below economical levels.

Lowering Cold Production Costs

To compete with offshore oil and absorb price differences between heavy and conventional oil production cost minimization is vital for the shallow (300 – 800 m) heavy oil reservoirs typical of Alberta and Saskatchewan Cretaceous deposit. Drilling costs can be lowered by using coiled tubing and smaller diameter drill hole; there is little evidence that a larger hole is better for cold production. Workover costs can be lowered by using better pumps that do not sand in, and by better workover methods to reduce service

TABLE 1: Enhancement of oil rate through cold production. Table Available In Full Paper.

rig time and re-establish sand production. Economic and environmentally acceptable sand disposal methods must be implemented(2). Finally, initial development must be planned with EOR production in mind to minimize additional redevelopment costs.

Cold Production Mechanisms

In these wells, conventional well theory predicts production rates of 0–2 m3/day, rather than the 5– 15 m3/day commonly obtained. Why does heavy oil flow more efficiently if 1–3% sand enters the wellbore with the fluids? A complete answer remains elusive, but the four major factors are likely enhanced drainage radius, grain movement, gas bubble expansion and continuous pore deblocking. Quantitative analyses have been developed for the first two(3, 4), and partly for the third mechanism(5). The fourth remains a qualitative concept.

Enhanced drainage arises because thousands of cubic metres of reservoir are affected by large-scale sand production. Discrete cavities may exist, piping tubes may develop, and zones dilated from 30% to 36–40% porosity may all accompany massive sand production. Each of these will increase well flow capacity. Closed-form solutions for piping tube or general yield models show that a factor of 3 to 4 in sustained rate productivity can be expected (3). However, improvement factors of 4 to 10 and more are common in cold production.

Grain mobility facilitates liquid movement, independent of permeability enhancement effects. A theoretical model of local fluid rate enhancement in mobile grain systems shows that increased flow rates up to a factor of two can be expected because of the reduction of drag forces(4).

There is a variant of the gas bubble theory which may help explain improved production(5).