1.1 Introduction
Lost circulation is a common drilling problem especially in highly permeable formations, depleted reservoirs, and fractured or cavernous formations. Lost circulation problems encountered during drilling is caused by the differential pressure of the hydrostatic column which is generally greater than the formation pressure, and is especially through the openings in the rock in low pressure or depleted zones. Circulation may be lost even when fluid densities are within the customary safety-margin; less dense than the fracture density of the formation. Stopping circulation losses before they get out of control is crucial for safe and economically rewarding operations (Abbas et al. 2004). Also, drilling through sub-salt zones poses a challenge to the operator because of the problem of lost circulation encountered in these zones.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research hypothesis and questions, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
Loss circulation is an old-aged problem normally encountered during drilling. It is one of the most time-consuming and costly problem faced by drilling industry. Loss circulation or loss of returns is defined as the drilling fluids into the formations which are usually lost to natural or induced formation fractures (Whitfill et al., 2008). After the lost circulation occurs, the level of drilling fluid in the annulus may drop and then stabilize at a particular level depending upon the formation pressure. The loss of drilling mud may results in increased drilling time, loss of expensive mud, plugging of productive formation, and or loss of well control (Arshad et al., 2014).
As the demand for petroleum resources increases, drilling of oil and gas wells are often carried out in challenging and hostile environments. Among the top ten drilling challenges facing the oil and gas industry today is the problem of lost circulation. Major progress has been made to understand this problem and how to combat it. However, most of the products and guidelines available for combating lost circulation are often biased towards advertisement for a particular service company.
Lost circulation is a broad subject and several studies and measures have been introduced in the industry to combat it. Moore (1986) stated that in areas such as below surface casing in normal-pressure formations where natural fractures are common, the most common method used to combat lost circulation is to drill without fluid returns to the surface. The purpose is to remove the generated cuttings from the hole and deposit them at the lost circulation zone. However, this practice requires large volumes of water and close supervision as there is the possibility of encountering high drill-string torque and drag.
The use of cement as LCM has also become a common practice while drilling and many researchers have investigated its use. Cement could provide a permanent cure for the problem and is irreversible in many cases. Therefore, it is generally applied to non-producing zones (surface drilling), in which mud loss is extremely severe, as a quick but permanent solution (Fidan et al. 2004).
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Practical Approaches for Solving Lost Circulation Problems While Drilling.
1.3 Statement of Problems
Investigation revealed that lost circulation is a common drilling problem especially in highly permeable formations, depleted reservoirs, and fractured or cavernous formations. The range of lost circulation problems begin in the shallow, unconsolidated formations and extend into the well-consolidated formations that are fractured by the hydrostatic head imposed by the drilling mud (Moore, 1986). Circulation may be lost even when fluid densities are within the customary safety-margin; less dense than the fracture density of the formation. Stopping circulation losses before they get out of control is crucial for safe and economically rewarding operations (Abbas et al. 2004).
1.4 Aim and Objectives of Study
The aim of the study is to examine the Practical Approaches for Solving Lost Circulation Problems While Drilling. In achieving this aim, the following specific objectives were laid out as follows:
- To evaluate the gelling characteristics of the system and test procedure for plugging capability;
- To provide the successes and the failures of the methods presented above in field applications; and
- To develop practical guidelines that is general and not biased towards a particular service company product.
1.5 Research Questions
The study came up with research questions so as to be able to ascertain the above stated objectives. The specific research questions for the study are stated below as follows:
- What is the gelling characteristics procedure of the system and test it’s plugging capability?
- What are the practical guidelines that are general and not biased towards a particular service company product?
