An Investigation of Drilling Mud pH Controlling Ability by Lignin

Graft Copolymer

Presented by

Mohamed Rashid Ahmed-Haras

Drilling Mud & Drilling Mud Additives

In the course of drilling an oil or gas well by means of rotary drilling tools, a so called ( Drilling mud ) is circulated downwardly through the hollow drill stem and bit to the bottom of borehole and then upwardly through the surface through the annular space between the drill stem and the interior of the borehole.

Cont ’’’

During the drilling process, drilling mud is applied to achieve specific functional :

Cool and lubricate the bit and drill string.

Transport cuttings to the surface.

Suspend drill cuttings in the annulus when circulation is stopped.

Support the walls of the borehole.

Stabilize the borehole.

This drilling mud system in which water is the continuous phase, also; this is the most common drilling mud used in oil drilling.

The most common mud used in the type is bentonite due to; its mixed friendly with water and allow mud additives to perform efficiently well. Beyond that, it is cheap.

A number of additives are used to alter the mud properties to fulfill all of the requirements of water-based drilling mud.

Both naturally occurring and synthetic polymers have been widely used. Among them, chemically modified biopolymer are probably one of the most extensively studied due to their low cost, lack of toxicity (Zhang, Tan & Li, 2001).

Cont ’’’

O

CHCH2n

HOOHC 100 C/ 18 Hrs

n

O C O

CH2 CH

OCH3

H2O

Polyacrylic acid Kraf t lignin

Lignin graf t copolymer

R

R

p-Toluenesulfonic acid

(A) H3CO

Chemical Modification of Lignin

Cont ’’’

Lignin Graft Copolymer (LGC)

Viscosifying agent Gelling agent

pH controlling agent

Rust retardant agent

Thermally stable up to 200 °C (16 hrs) with 0.5 % w/w

Cont ’’’

Noteworthy, most of the drilling mud additives are alkaline in pH which requires to be adjusted to desired pH range via pH controlling agent. Interestingly, lignin graft copolymer (LGC) which is a modified bio-polymer has rheological controlling property in tandem with an acidic character that may minimize the use of pH controlling agents. Hence, the present study evaluates the pH controlling ability of LGC.

Cont ’’’

Table 1: Basic mud pH values under different aging temperature

Types of Mud T (oC) pH

Base Mud + 0.3% LGC 27 10.49

Base Mud + 0.5% LGC 27 9.63

Base Mud + 0.7% LGC 27 7.45

Base Mud + 0.3% LGC 90 10.15

Base Mud + 0.5% LGC 90 76

Base Mud + 0.7% LGC 90 60

Table 2: comparative evaluation of LGC and commercial additives at 200 ˚C for 16 hours

Types of mud pH

Before After

Base mud + 0.5% LGC 9.65 9.25

Base mud + 0.5 % CMC 11.62 9.30

Base mud + 0.5 % Guar Gum 11.53 8.73

Base mud + 0.5 % Xanthane 11.62 8.64

Cont ’’’

As the LGC concentration increases in the drilling mud samples, the pH value decreases. This acidification affect of the LGC could be results from two causes. First, the acidification effect might be due to the use of sulphuric acid during the separation process of the Kraft lignin from the other wood components.

The other cause might possibly be corresponding to the branched acrylic monomer in the LGC structure and the present of functional groups such as hydroxyl, carbonyl, and ester as illustrated in FTIR spectrum. That might give the acidic character to LGC when it was used as a drilling mud additive.

O

CHCH2n

HOOHC 100 C/ 18 Hrs

n

O C O

CH2 CH

OCH3

H2O

Polyacrylic acid Kraf t lignin

Lignin graf t copolymer

R

R

p-Toluenesulfonic acid

(A) H3CO

Cont ’’’

Acrylic group

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0cm-1

%T

Lignin graft copolymer

Kraft lignin

Acrylic acid

3418.73

2920.81

2489.35

1919.15

1601.461497.15

1398.04

1188.391132.19

1068.89

1044.71

1013.38

884.99850.36

814.93697.47

614.42

569.40

453.551723.07

3415.48

2935.26 1713.57

1616.03

1518.731463.19

1426.95

1143.21

995.77

822.96

636.75

622.78

3235.66 2973.921637.031619.16

1410.81

1299.23

1183.861060.23

987.08810.77

668.15

Cont ’’’

LGC has been successfully synthesized by exploiting the waste of palm oil industry via the polymeric technique.

Among all LGC concentrations which have been evaluated, only 0.5% w/w of LGC maintained the pH of the water-based mud within the desired pH range.

From an experimental point of view, the use of 0.5 % LGC as drilling mud additives is not required any additional additives pH controlling agent (soda ash and acetic acid), thereby it may reduced the cost of drilling operation and minimize the environmental damage.