Planning the drilling fluids program is one of the most important steps in Planning the drilling fluids program is one of the most important steps in preparation for the drilling of a welt Many factors influence the type and preparation for the drilling of a welt Many factors influence the type and properties of the fluid required. properties of the fluid required. This paper will outline some of the drilling problems that may be encountered in Southeast Asia; brief methods of anticipating these problems before they occur are developed. Techniques for dealing with various drilling problems through engineered drilling fluids program are discussed. In particular, the application of controlled salinity oil muds and the use of salt polymer mud systems for improved borehole stability, solids control, corrosion reduction, safety and economy, are emphasized. Current trends and developments in drilling fluids systems are discussed.
Planning the drilling fluids program in Southeast Asia is Planning the drilling fluids program in Southeast Asia is similar to the same task any place in the world. The conditions one can expect to encounter vary from no-problem normal pressure situations to the impractical-to-drill high pressure, high temperature, completely unstable borehole pressure, high temperature, completely unstable borehole conditions such as reported by Ferti, Blake and Gray. 2 and 3.
It is a commonly accepted estimate that more than 80% of the exploration wells drilled in Southeast Asia do encounter severe hole problems, resulting in the loss of valuable data and time, and preventing proper evaluation of a prospect. The loss of a hole is not uncommon.
Historically, drilling fluid development saw improvements in controlling drilling fluid properties with little regard to effect on drilling. Causes of borehole problems were not understood and cures were often worse than the ailment.
A better understanding of the basic causes of hole instability has led to new approaches being taken to eliminate or reduce problems. problems. There has also been a tendency in the past and even today to base the choice of mud system on only one to two criteria, such as low cost, availability, or ease of running, rather than on a scientific evaluation of all facets involved. In many cases the lowest cost drilling fluid system may not yield the lowest cost well drilled.
If cost, environmental factors, and geological information were of no consequence, problem wells could be drilled with invert emulsion muds. This is not the case. A drilling fluids program must be designed to give maximum information, program must be designed to give maximum information, along with maximum hole stability at the lowest cost possible. This can only be attained if all factors are considered and the drilling fluid designed accordingly.
The first step in planning any drilling fluids program is to gather all available data, such as geological seismic, and offset well information, to determine what conditions may be encountered in penetrating the section.
With this information, decide what the specific problems are for the area and location in question. Consider briefly the depth of interest, lithology, pressures, temperatures, logistics, drilling equipment available, and qualifications of supervisory personnel assigned. personnel assigned. Choose the best drilling fluid type available for each phase of the hole programmed based on engineering and economic studies and considering the hazards of drilling expected, the cost of time lost due to unstable hole, availability of materials, and expertise to formulate and maintain the fluid.
Divide the program into phases by drilled hole size, indicating the expected problems, the fluid properties range required, and the material concentration range estimated for each unit volume of drilling fluid consumed.
Estimate the material requirements for each phase based on maximum consumptions, planning ample contingencies to cover any logistic problems or unpredictable hole conditions. Cost estimates and shipping tonnage/volumes for the well's total material requirements should be calculated.
In an effort to expand on a method of planning the drilling fluids program by scientific, logical steps the following considerations are put forward.
When a wellbore penetrates a sedimentary section it interrupts a process of physical and chemical change which has been going on for considerable time. Being penetrated by a drilling bit comes as something of a shock to these formations. The drilling process relieves pressure on the rocks at the borehole and the drilling fluid exposes them to an alien chemical environment.
The average geologic section through which most wells are drilled consists of mainly shale, with sands and sometimes limestone or coal. Most drilling problems are derived from the shales. These are basically unstable rocks, composed of clay minerals which are compressible and water degradable. With depth of burial and increased temperature the clay minerals present at the surface are subject to alteration.