Instant Data for Mud Logging Applications

One of the biggest mining industry challenges is finding oil and natural gas reservoirs. A tremendous amount of time and money can be lost without the right tools, data, and technology to quickly target the best drill sites. Oil and gas exploration begins with a search for the structural landmarks characteristic of a deposit such as anticlinal slopes, but more conclusive data must be gathered from a variety of sources before a decision can be made about whether or not to start drilling. Chemical analysis of outcrops and cuttings are used to determine the composition of rock and infer mineralogical properties favorable to oil and gas exploration and production. Another important technique in oil and gas exploration is inferring lithology, or mud logging, the practice of examining rock chips that are brought to the surface by circulating drilling media (most commonly mud). Mud logging is a technique to help geologist pinpoint the most productive strata and avoid drilling in the wrong spot by:

• Identifying downhole lithology (rock type)
• Marking positions of hydrocarbons with respect to depth
• Confirming that conditions are suitable for drilling
• Guiding geo steering—steering the drill bit in real-time based on geological data
• Monitoring natural gas entering the drilling mud stream
• Determining the appropriate drilling equipment to be used
• Creating well logs.

The rock chips produced by mud logging are identified by examining thin sections of the rock under optical microscope. This method is time consuming and requires a thin section preparation laboratory onsite. There is no instrumental technique to identify rock type directly. Off-site laboratory analysis methods such as x-ray diffraction (XRD) and Raman spectroscopy can identify the mineral composition of rocks but may take weeks, or even months to produce useful data. Now, these techniques are complemented by field portable x-ray fluorescence (FPXRF), a technique that is gaining momentum and acceptance in addressing applications in various fields in geology and mining including oil and gas exploration and production. FPXRF can analyze a variety of sample types which are common in the oil and gas upstream exploration and production (E&P) industry including drill cuttings, oil and gas cores, outcrops, and piston cored sediments. FPXRF is not only be used to identify elemental composition, but also the subtle changes in geochemistry of reservoir rocks and monitoring of the gradual transition from one rock type to another. The geochemical data from these analyses can be used for several applications in addition to mud logging, including inferring mineralogy, chemostratigraphy, reservoir characterization, and oil and gas productivity. Although FPXRF analyzers cannot analyze hydrocarbons, they can be used to characterize reservoir properties that influence porosity (cements), permeability (clays, cement type), fracture population (Si content), and productivity (e.g. V, Cr, Mo content). Most importantly, FPXRF instruments are operated in the field and provide analysis within seconds to enable quick decisions about whether or not to drill, where to focus, and when to send a sample for further analysis. Our next article will address a case study summarizing the results of FPXRF analysis conducted on 221 samples collected from an oil and gas drill site in Southeast Asia.