THE EFFECTS OF CONTAMINANTS ON THE FLOW OR RHEOLOGICAL PROPERTIES OF OIL BASED MUD

CHAPTER ONE

INTRODUCTION

 

1.1     Background of Study

Drilling for oil and gas with a drilling mud began many years ago in the 18th century. The first reported use of a drilling fluid was noted in France in 1845, when water was pumped down a hollow boring rod, while drilling water wells to bring the cuttings from the bottom of the well to the surface. (Ikeh, 2014)

 

Through the 1920's Iron oxide and Barium Sulphate (Barite) was used to increase the density of the drilling mud, thus preventing entry of the formation fluid into the borehole. The use of bentonite in 1930's to suspend Barite formed the basis for today's large commercial drilling mud industry. (Evabeta, 2004)

 

The term "drilling fluid" includes air, gas, water and mud or could either be a combination of two or all the above. The common type of fluid most often used in mud suspension of solid clay is a liquid and emulsion mud (suspension of solid and droplets of liquid). The drilling fluid is a term that comprises all the components of clay and additives suspensions used to effect the removal of rock cuttings from the subsurface (bottom hole) to the surface while drilling.

 

Thus, in other to enhance the drilling operation, the selected drilling mud must perform certain functions to avoid delay in operation and occurrence of associated drilling problems. Some of these functions are highlight below.

 

1.1.1  Functions of drilling fluids

 

Lubricate  the  drill  bit,  string,  bearings,  mud  pump  and  drill  pipe,  particularly  as  it  wears against  the  sides  of  the  well  when  drilling  deviated  wells  around  corners.  Clean  and  cool  the  drill  bit  as  it  cuts  into  the  rock. Lift  rock  cuttings  to  the  surface  and  allow  cuttings  to  drop  out  in  the  mud  pit  or  shakers  to prevent  them  re-circulating.

  IV.            Suspend cuttings and weighting material when circulation is interrupted

Protect the formation from caving Provide  information  to  the  drillers  about  what  is  happening  down  hole  by  monitoring  the behavior,  flow  rate,  pressure  and  composition  of  the  drilling  fluid. Prevent  well  blow-out  by  including  very  heavy  minerals  such  as  barite  (weighing  agent)  to counteract  the  pressure  in  the  hole  (reservoir  pressure). Drilling  mud  helps  in  suspension  of  drilling  assemble  and  casing,  delivery  of  hydraulic energy,  being  a  suitable  medium  for  logging  and  to  being  environmentally  acceptable.