How To Flood a Tight Sand
Authors: Sloat Ben , Brown Maurice 
Published: December 2007

The Moore-Holverson-Hill-Aagard waterflood is followed from 1963 start-up to Jan., 1968. The Bartlesville sand body is marginal by normal waterflooding standards, but secondary oil recovery to date and production trends point to an ultimate recovery that will be twice the point to an ultimate recovery that will be twice the average for other "successful" floods in the county. Water quality, wettability and treatment with polymer are documented. Special emphasis is placed on the amount of extra oil produced from areas effected by polymer. Over-all project economics are presented, and the impact of project economics are presented, and the impact of polymer treatment on Aagard lease performance and profit are polymer treatment on Aagard lease performance and profit are studied in detail.

Introduction

In Southeastern Kansas where waterflooding has been conducted for over 20 years, the better quality reservoirs are gone. Only the marginal prospects are left. Our purpose is to show that good operation, modern petroleum purpose is to show that good operation, modern petroleum engineering, and sound water handling now make it possible to successfully flood many of these marginal sands. possible to successfully flood many of these marginal sands. The paper will outline the early history of the reservoir, detail conditions at the start of the flood, and describe input well behavior and production responses on the Moore and Aagard leases. It will also deal with attempts to "tailor" injection water for better oil recovery. Some of the efforts made during this 4-year study period are destined for the technological junk pile. Several show promise, and one - the highly selective use of polymers promise, and one - the highly selective use of polymers has been very effective.

The wide range of crude oil properties and producing formations makes it hard to see water as the best displacing fluid. Yet most decisions concerning source water are based on volume, year-around supply, and corrosion- or scale-forming tendencies. No thought is given to how well the water will displace oil. The objective of the "water treatment program" is to move the fluid from surface to formation without dissolving the lines or plugging so much that pressures go above wellbore limits. It is assumed that once pressures go above wellbore limits. It is assumed that once water moves beyond the inputs its ideal properties take charge and start to move oil toward the producing wells.

A good flood water would behave very much like the oil it is trying to displace. Table 1 shows important differences in Bartlesville' crude oil and water. A big unknown is the wetting nature of the two fluids.'

Changing water properties to improve oil displacement has been done in the laboratory. When costs enter the picture, field tests are usually turned down. This is because picture, field tests are usually turned down. This is because reservoir rocks represent a huge surface area, and any product added to water to effect a wetting change would be product added to water to effect a wetting change would be absorbed on a small portion of this surface and all further benefit would be lost. However, there is another side to this argument. Water travels from high pressure pump to input wellbore in a few hours and on the way may contact 5,000 to 10,000 sq ft of a known surface. Those who have back-flowed input wells know that important water changes can take place during this short contact time. The trip from input to producing well takes months (or should), and millions of square feet of surface area are contacted. The nature of this surface is largely unknown and all sorts of water-rock equilibria are possible. Because of the large surface area involved, even the slightest reaction can be important, so that a purposeful, though minute, change in water properties can exert great influence on oil recovery.

Greenwood County is the third largest secondary oil producing county in Kansas. Most production comes from producing county in Kansas. Most production comes from the Bartlesville sand, which was started under flood in the late 1940's. Secondary oil from the Bartlesville has averaged 90 bbl/acre-ft. Properties of the Bartlesville sand are shown in Table 2. Column 1 is the average of 12 successful water floods. Column 2 is the same data for the Moore-Holverson-Hill-Aagard (MHHA) unit after 4 years of development and operation. By any of the standard yardsticks, the project should be a marginal waterflood. Water saturations are high and oil in place is low. The reservoir is small and the permeability is only about one-tenth of that normally found. Primary recovery was also poor. Although data for all 12 projects are not available, poor. Although data for all 12 projects are not available, six of the 12 studied produced less than 20 bbls/acre-ft ahead of a producing water-oil ratio (field-wide) of 2.