New Process for Plugging Abandoned Wells

Description:

Table of Contents

1. Introduction and Project Goals
2. Work in Progress
3. Sample Collection
4. Chemical Analysis
5. Particle Size Distribution
6. Development of Methodology for Fly Ash Formulation
7. Plans for the Next Quarter

1. Introduction and Project Goals

Cement grout is the present material used in plugging the abandoned wells. Fly ash is known to have properties very similar to cement and can be produced with strength similar to cement grout. Blends of fly ash (especially the less cementitious Class F fly ash) and cement have been used in the oil industry since 1950. Presently, only about half of the fly ash produced by the various coal-burning power plants in the state of Oklahoma is used in cementing applications. The remainder must be treated as a waste product and disposed of in landfills.

Much of this fly ash is the higher lime content, more cementitious, Class C fly ash. The objective of this research is to show that Class C fly ash can be retarded like cement when slurried and, further, that it can be pumped and placed like cement with coiled tubing instead of employing a rig. This will prove the concept of utilizing this kind of setup for wells where it will apply. On wells where there is a means of handling pipe, mixing and pumping, only the plugging material will be required. The optimum formulation developed will be suitable for both the coiled tubing and jointed pipe applications.

The specific objectives of this project are to obtain the cementitious properties of Class C fly ash from five coal-fired power plants in Oklahoma and, utilizing these properties, to produce a fly ash grout similar to cement grout. Furthermore, the ability to pump this slurry through coiled tubing to place a plug of fly ash grout will be proven. The end result is to utilize a fly ash grout for plugging of abandoned oil, gas, and water wells rather than a cement grout. The research is divided into two phases: (1) laboratory analysis of samples of the fly ash from selected power plants and development of optimum grout formulations, (2) the pumpability of these formulations through coiled tubing and straight pipe will be proven and the frictional properties investigated.

2. Work in progress

Planned	Progress	Task completion date
Samples Collection	Collected samples from the following power plants in Oklahoma Oogah Muskogee Oklaunion Hugo Red Rock	Jan. 23, 2001
Chemical Analysis	Performed Chemical analysis of samples with ASTM C 618 - three replications	Dec. - Feb. 2001
Particle size distribution	Performed sieve tests for the particle size distribution with ASTM C 136	Feb. 2001
Method development to reduce friction pressure loss	In progress for developing the optimum formulation of fly ash Compressive strength tests with API Spec 10 and Spec 10A	Feb - April 2001

3. Sample Collection

Five different fly ash samples for laboratory tests were collected from the following sources. In order to maintain the test consistency and to conduct various tests with the same samples, enough volume of samples (2 buckets - 5 gallon each) were collected.

Power Plants

1. Oologah

Agent: Mineral Solutions, Inc.: 1949 E. Sunshine Suite 2-220
Springfield, MO 65804

2. Muskogee

Agent: Mineral Solutions, Inc.: 1949 E. Sunshine Suite 2-220
Springfield, MO 65804

3. Oklaunion

Agent: Boral Material Tech, Inc.: 45 Northeast Loop 410 Suite 700

San Antonio, TX 78216

4. Hugo

Agent: Holnam: 1100 W 18th Street
Ada, OK 74820

5. Red Rock

Agent: Mineral Solutions, Inc.: 45 Northeast Loop 410 Suite 700
San Antonio, TX 78216

4. Chemical Analysis

Chemical analysis was performed with the ASTM C 618 "Fly Ash and Raw or Calcined Natural Pozzalan for Use as a Mineral Admixture in Portland Cement Concrete" Class C requirements with three replications. One chemical replication test required one month according to this standard. The details of the test and analysis will be included in Annual Report.

5. Particle Size Distribution Tests

The objective of these tests is to determine particle size distribution of each fly ash source. These data will be used to develop relationship concerning surface area of particles and the required water volume. The test standard applied in these tests was ASTM C 136 "Sieve Analysis of Fine and Coarse Aggregates". Retsch Sieve Shaker and US standard fine mesh sieves (#140 to #400) were used with the following test conditions (Fig. 1).

• Amplitude: 80 %
• Duration: 10 min.
• Sample weight: 100 gm.

6. Development of Methodology for Fly Ash Formulation

To provide the optimum formulation of fly ash, which can produce pumpability and high compressive strength, the tests with various formulations with three replication samples are under progress.

6.1 Test Procedure

The procedures defined in Section 7 of API Spec. 1 (1990) and Section 8 of API Spec. 10A (1995) have been applied on this test. Three samples have been cured in water curing bath controlled at 120oF (( 3oF). The samples are tested by the hydraulic testing machine (Carver lab Press), of which hydraulic capacity is 0 - 20, 000 lbf (Fig. 2).

6.2 Sample Preparation

Plastic coated 2-in. diameter paper mold was used to make samples for compressive strength tests. Grease is thinly applied on the interior faces of the molds and the contact surfaces of the stainless plate. The contact surface of the halves of each mold was also coated with grease to make the joint water tight when assembled. Excess grease was removed from the interior surface of the assembled molds. The molds were placed on a thinly greased stainless plate. Grease was also applied to the exterior contact line of the mold and the base plate.

6.3 Slurry Preparation

Eight hundred grams of fly ash sample was weighed by using the electronic scale having 0.01 gram accuracy. Water was weighed by graduated glass cylinder according to the Section 5.3 of API Spec. 10. Retarder and/or dispersant were added in the water while agitating in the mixer.

6.4 Test Results

Presently, the compressive strength tests with various formulations are under way. The test results and their analysis will be included in the Annual Report.

7. Next Quarter Plans

7.1 Development of methodology for the fly ash formulation

Through the compressive strength tests with various formulations, the optimum formulation of the fly ash will be determined. The compressive strength tests will be performed under the different curing times: 24 hrs, 48 hrs, and 1 week. The compressive strength will be calculated by dividing the maximum load in lbf by cross-sectional area in square inches. The dimensions of the test faces will be measured to ( 1/16-in. (1.6 mm) for calculation of the cross-sectional area. The rate of load increase will be 400 psi per minute for specimens expected to have greater than 500 psi strength. For specimens expected to have less than 500 psi strength, 100 psi increment per minute will be applied. The compressive strength will be recorded and averaged to the nearest 10 psi. The weight percent of dispersant and retarder will be adjusted by the results of thickening time test.

7.2 Thickening time tests

The elapsed time between the initial application of pressure and temperature of the apparatus and the occurrence of a consistency of 100 Bc will be reported as the thickening time for the test. The maximum consistency during the 15-30 minutes stirring period will be reported. The acceptance requirements for the maximum consistency during the 15-30 minutes stirring period will be 30 Bc for fly ash cement formulations in accordance with API RP 10A.