DRILLING MUD , A VITAL ROLE WHEN DRILLING OIL WELL
ABSTRACT
Drilling mud plays an important role when drilling an oil well, where it produces sufficient hydrostatic pressure that could prevent the influx of formation fluids into the well bore. Currently, Barium sulphate (BaSO4) also known as barite is widely used as weighting agent in drilling fluids slurry to ensure proper weights are achieved. With the expected increase in drilling activities and the dwindling reserves of barite, its supply may fall short in the foreseeable future. This study was carried out to access the prospect of utilizing galena, a lead-based mineral, as an alternative weighting material in drilling fluid. The mud formulation comprised water, bentonite and weight materials, weighted to desired densities. During mud analysis, amongst the parameters investigated were density, rheological properties and solid content. The result show that galena mud sample gave a little higher yield point and gel strength than barite mud sample. At 9.0ppg, the yield point of galena was 20.0ℓb/100ft2 and barite 22.0ℓb/100ft2 while the 10 second gel strength of galena was 5.0ℓb/100ft2 and 8.0ℓb/100ft2 for barite. Similarly, little difference was observed in plastic and apparent viscosities. At 9.0ppg, the plastic and apparent viscosities of galena were 13.cp and 23.0cp while barite was 10.0cp and 20.cp. At 15.0ppg, the plastic viscosity of barite was higher than galena. Compared to galena, barite gave higher solid content. At 9.0ppg, solid content of galena was 3% and barite was 5%. The suspected acidic mud of galena was buffered at a favorable alkalinity with caustic soda. A significant advantage could be realized via galena; it produces lower solid content which in turn increases rate of penetration. Greater tolerance to drill solids should reduce overall mud and well costs. Based on this preliminary study, it is concluded that galena has the potential to be used as weighting material in drilling mud.
Chapter One
Introduction
1.1 Background of the Study
Drilling fluid may be defined as a suspension of solids in a liquid phase. In petroleum engineering, drilling fluid is a fluid used to drill oil and gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. Liquid drilling fluid is often called drilling mud. The three main categories of drilling fluids are water-based mud (which can be dispersed and non-dispersed), non-aqueous mud, usually called oil-based mud, and gaseous drilling fluids, in which a wide range of gases can be used.
The main functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering into the well bore, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, and suspending the drill cutting while drilling is paused and when the drilling assembly is brought in and out of the hole. The drilling fluid used for a particular job is selected to avoid formation damage and to limit corrosion.
Before oil can be produced from a reservoir, an oil well has to be drilled first in order to furnish a conduit between the reservoir and surface. When an oil well is being drilled, drilling mud has to be used in order to carry drill cuttings to surface, to cool the drilling bit and also to provide sufficient hydrostatic pressure across the high pressure zones. Practically, the hydrostatic pressure has to be 250 psi (1,724kpa) to 450 psi (3,103 kpa) higher than the formation pressure. Failure to furnish sufficient hydrostatic pressure across the zones will cause influx of formation fluids, and this phenomenon may lead to blowout if the influx conduit be stopped in a relatively short time.
In drilling an oil well, barite is the predominant weight material used. In modern drilling fluids, of all additives used in the formation of oil well drilling fluids; the weighting material is the largest in quantity used. Barite is also used in many other applications including, as a filler and weight material for paints, rubbers, plastics, brake pads in automobile industry and as an additive in paint prime for gloss and protection.
In generally barite is not considered harmful when used in accordance with recommended work place precautions and is usually deemed safe. In almost all geographic areas, drilling grade barites are environmentally acceptable from the stand point of disposal as part of the drilling fluid (Bruton et al, 2006).
Barite used in oil industry is regulated for chemical purity as it is recognized that some sources of barite may contain heavy metals ranging from trace amounts to some exceeding 3% by weight. By far, however, barite is most widely used in drilling fluids as primary density adjustment or “weight up” additive. Drilling barite is appealing over other choices in weighting material due to its generally benign characteristics. Its consistency and quality allows its use as a density increasing agent imparting mineral impact on most drilling fluids. Barite has high specific gravity which permits weighting the mud with a little increase in solids. Its chemical inertness and virtual insolubility in water or oil minimize effects on mud properties and the environment. Also, barite intermediate hardness is soft enough to prevent serious abrasion of metal but hard enough to prevent the excessive attrition and creation of fines. Its availability in large quantity at low cost to meet the industry requirement for millions of tons per year makes it generally acceptable (Bruton et al, 2006).
1.2 Statement of the Problem
Barite is the predominant weight material used in modern drilling fluids. Of all additives used in the formulation of oil well drilling fluids, the weighting material is also the largest in quantity used.
Like most years, the world’s barite mining industry in 2005 produced a total exceeding 7 million tons barite ore (Bruton et al, 2006). The barite was processed primarily to become a weighting agent for drilling fluid and experienced decrease in reserve due to high rate of exploitation. The decline of relatively barite powder that meets API’s standard minimum density specification of 4.20 units, specific gravity is on the horizon in the market. Consequently, prudent and relatively straight forward actions, if initiated soon, will mitigate otherwise inevitable dramatic future cost increases. Timely actions, if engaged will assure that premium drilling fluid systems can be weighted economically and still meet the various technical requirement of the drilling industry well into the future. Therefore, the global use of barite instills fear of rapid depletion signified by dwindling nature of the reserve.
Many recent developments in drilling mud technology make for difficult choices. Formations to be drilled vary tremendously both as to mineralogical composition and stress conditions. Unsuccessful mud control will be plagued with time consuming and costly problems such as kick and blowout, hole enlargement, sloughing of well bore or general instability of the well bore. Because of the expected shortage and possible cost savings, a research program is initiated to investigate the possible weight materials.
1.3 Objectives of the Study
This work tries to look at:
- i) The suitability of using galena instead of barite as weighting agent in drilling fluids.
- ii) To investigate the performance of galena as weight material.
iii) To identify problem areas that occurs when galena is used and proffer solutions
1.4 Significance of the Study
The demand for high quality barite as drilling fluid weight material is expected to be increasingly difficult to meet. In addition, the supply of the barite is geographically limited, with high transportation costs of the expected shortage and possible cost savings, a weighting material that can be economically substituted for barite and that can influence penetration rates would be received in the industry; since it plays important role in well cost reduction. The challenge of providing existing quality barite at reasonable and acceptable costs is ever increasing. High consumption coupled with depleting supply of acceptable material and economic factor associated with mining, grinding and transporting barite globally necessitates study and pre-emptive ways to sustain cost-effective supply.
The study will provide useful information about the properties that will qualify galena, a lead-based mineral from Awe, Nassarawa state, to be used as barite substitute. Through this study, the major causes of reduction in mud weight during drilling and its effects caused by this reduction will be recognized and managed effectively.
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