Kamal Abdurahman

Group:B

2/7/2015

2015Mud Filtration

Supervised By : Mr.Pshtewan Jaf Mr.Sarhad

Mr.Goran

FACULTY OF ENGINEERING

SCHOOL OF PETROLEUM AND CHEMICAL

DRILLING ENGIEERING LAB

Aim of experiment:

The test consists of monitoring the rate, at which fluid is forced from a

filter press under specific conditions of time, temperature and pressure,

then measuring the thickness of the residue deposited upon the filter

paper.

Introduction

The filtration and wall building characteristics of a drilling mud are important

for providing a relative measure of the amount of mud filtrate invasion into a

porous and permeable formation and the amount of filter cake that will be

deposited on the wall of the well bore wherever filtration occurs. From a

drilling viewpoint these properties give an indication of the amount of water

(or oil) wetting that can take place in filtrate sensitive formations and the

potential for tight hole or differential sticking problems. For productive,

hydrocarbon bearing formations these properties give an indication of the

amount of filtrate invasion and permeability damage that can be expected.

Theory

Loss of fluid (usually water and soluble chemicals) from the mud to the

formation occurs when the permeability is such that it allows fluid to pass

through the pore spaces. As fluid is lost, a build up of mud solids occurs

on the face of the wellbore. This is the filter cake.

The loss of liquid from a mud due to filtration is controlled by the filter

cake formed of the solid constituents in the drilling fluid. Two types of

filtration occur; dynamic, while circulating and static, while the mud is at

rest.

Dynamic filtration reaches a constant rate when the rate of erosion of the

filter cake due to circulating matches the rate of deposition of the filter

cake.

Static filtration will cause the cake to grow thicker with time, which

results in a decrease in loss of fluids with time.

Filtration tests are conducted under two different conditions:

1 .The standard API filtration test is conducted at surface (or room)

temperature and 700 kPA, (l00 psi), pressure for thirty minutes. For this

test the fluid loss is the volume (in millilitres) of filtrate collected in this

time period and the filter cake thickness (in millimetres) is the thickness

of the cake that is deposited on the filter paper in this time period .

2 .The API high temperature, high-pressure test, (HTHP test) is

conducted for thirty minutes of filtration at a temperature of l49 C, (300

F), and a differential of 3450 kPa, (500 psi). For this test the filtrate must

be collected under a backpressure of 700 kPA, (l00 psi) in order to

prevent vaporization of the filtrate.

Apparatus of experiment

Equipment:

Standard Filter Press

Procedure

1 .Be sure each part of the cell is clean and dry, particularly the screen,

and that the gaskets are not distorted or worn. The screen should be

free of sharp edges, burrs or tears.

2 .Assemble the cell as follows: Base Cap, rubber gasket, screen, one

sheet of filter paper, rubber gasket and cell body .

3 .Pour the freshly stirred sample of fluid into the cell to within 0.5 inch

(13 millimeters) to the top in order to minimize CO2 contamination of the

filtrate. Check the top cap to insure the rubber gasket is in place and

seated all the way around and complete the assembly. Place the cell

assembly into the frame and secure with the T-screw .

4 .Place a clean dry graduated cylinder under the filtrate exit tube .

5 .Close the relief valve and adjust the regulator so that a pressure of

100 ± 5 pounds per square inch (690 ± 35 kilopascals) is applied in 30

seconds or less. The test period begins at the time of initial

pressurization .

6 .At the end of 30 minutes, measure the volume of filtrate collected.

Shut off the air flow through the pressure regulator and open the relief

valve carefully .

7 .Report the volume of filtrate collected in cubic centimeters to the

nearest 1/10th centimeter3 as the API filtrate. Report the time interval

and the mud temperature in °F (°C) at the start of the test. Save the

filtrate for running chemical analysis .

8 .Check to see that all pressure has been removed from the cell, and

then remove the cell from the frame. Disassemble the cell, discard any

remaining mud and using extreme care save the filter paper and

deposited cake with a minimum of disturbance to the cake. Wash the

filter cake on the paper with a gentle stream of water or with diesel oil if

oil mud is being tested .

9 .Measure and report the thickness of the filter cake to the nearest 1/32

inch (0.8 millimeter). A cakethickness less than 2/32 inch is usually

considered acceptable. Observations as to the quality of the cake should

be noted. Notations such as hardness, softness, toughness, slickness,

rubberiness, firmness, flexibility and sponginess are appropriate

descriptions.

Discussion

Effect of mud filtration on formation damage:-

Formation damage

is an undesirable operational and economic problem that can occurs during the various

phases of oil and gas recovery from subsurface reservoirs including production, drilling,

hydraulic fracturing, and work-over operations. Formation damage assessment, control,

and remediation are among the most important issues to be resolved for efficient

exploitation of hydrocarbon reservoirs.

Deep bed filtration of fines with capture and permeability damage takes place near to

production wells, in drilling operation. The particles in drilling fluid are captured by size

exclusion (straining) or by different attachment mechanisms (electric forces, gravity

segregation and diffusion).

Mud cake occur when:-

The residue deposited on a permeable medium when a slurry, such as a drilling fluid, is forced

against the medium under a pressure. Filtrate is the liquid that passes through the medium,

leaving the cake on the medium. Drilling muds are tested to determine filtration rate and filter-cake

properties. Cake properties such as cake thickness, toughness, slickness and permeability are

important because the cake that forms on permeable zones in the wellbore can cause stuck

pipe and other drilling problems. Reduced oil and gas production can result

from reservoir damage when a poor filter cake allows deep filtrate invasion. A certain degree of

cake buildup is desirable to isolate formations from drilling fluids. In open hole completions in high-

angle or horizontal holes, the formation of an external filter cake is preferable to a cake that forms

partly inside the formation. The latter has a higher potential for formation damage.

-Excessive filtration and thick filter cake build up are likely to cause the

following problems:

Tight hole, causing excessive barrier. Increased pressure ,due to reduced hole diameter.

Differential sticking, due to an increased pipe contact in filter cake.

-Pressure affects filtration by:

Compressing the filter cake, reducing its permeability and therefore reducing the filtrate.

-Temperature affects on filtration by:

Reducing the viscosity of the liquid phase and hence increasing filtration.

-Time affects on filtration:

With all other factors being constant, It has been found in early work that the volume of

fluid lost is roughly proportional to the square root of the time for filtration.

-Form of mud cake and mud filtration with time cause to occur of formation damage:

Formation damage is defined as the impairment to reservoir (reduced production) caused by

wellbore fluids used during drilling/completion and workover operations. It is a zone of

reduced permeability within the vicinity of the wellbore (skin) as a result of foreign-fluid

invasion into the reservoir rock.

-Preventing formation damage:

1-Ability to recover fluids from the reservoir is affected very strongly by the hydrocarbon permeability in the near-wellbore region

2-Although we do not have the ability to control reservoir rock properties and fluid properties, we have some degree of control over drilling, completion, and production operations

Reference

Payatakes, A.C. et al., “Application of Porous Medium models to the Study of Deep Bed Filtration,” Can. J. Chem. Eng., 52, 727 (1974).

Jiao, D. and M.M. Sharma, “Mechanism of Cake Buildup in Crossflow Filtration of Colloidal Suspensions,” Journal of Colloidal and Interfacial Science, 1994. 162:p. 454-462.

http://www.glossary.oilfield.slb.com/en/Terms/m/mudcake.aspx

Fisk, J.V., and Jamison, D.E., "Physical Properties of Drilling Fluids at High Temperatures and Pressures," SPE Drilling Engineering, December 1989, pp. 341-46.