New System Provides Continuous Quantitative Analysis of Gas Concentration in the Mud During Drilling
- G.L. Roberts (Anadrill Schlumberger) | V.C. Kelessidis (Anadrill Schlumberger) | J.M. Williams (Anadrill Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- September 1991
- Document Type
- Journal Paper
- 219 - 224
- 1991. Society of Petroleum Engineers
- 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.3.4 Scale, 1.12.1 Measurement While Drilling, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.12.3 Mud logging / Surface Measurements, 4.6 Natural Gas, 5.6.1 Open hole/cased hole log analysis, 5.1.1 Exploration, Development, Structural Geology, 5.4.2 Gas Injection Methods
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Continuous monitoring of hydrocarbon gases in drilling fluids at the surface is essential for identification of prospective reservoir zones as well as for safety. This paper describes a new gas-analysis system that determines the total amount of gas in this mud below the bell nipple. The system is continuous, consistent, and fully quantitative (unlike a gas trap) but not labor-intensive (like a steam still). It also recovers and analyzes gas liberated into the air at the bell nipple, which test results have shown to be almost 50% of the total gas in the mud below the bell nipple.
J.T. Hayward, the "father of mud logging," once said, .... it is for the fluid contents, rather than for the rock itself, that wells are drilled." That statement still applies today, although mud logging is now viewed as a "low-tech" operation when compared with measurement-while drilling (MWD) and wireline techniques. Conventional mud logging has been around for more than 50 years and has proved to be a valuable service. For example, gas- or oil-bearing sections can be detected while drilling, and other information obtained through mud logging can be useful in determining coring and casing points and can indicate over- or underbalance drilling, an important safety consideration. Existing services typically provide a continuous reading of total hydrocarbons, with chromatographic analysis to give the concentrations of individual components. Interpretation packages use either the hydrocarbon concentration or component ratios to determine the quality of the formation fluid. The major drawback with the current system is that the data are effectively qualitative because vast errors are involved. "If representative samples are not obtained, the potential value of mud logging is seriously compromised." A survey conducted by Anadrill indicated that the geologist's main use for mud-logging services was hydrocarbon detection and show evaluation; however, the area that was considered the industry's weak point was gas measurement.
When a well is drilled, a crushed increment of rock and any contained fluids are released and transported to the surface by the drilling fluid. Removing all these formation fluids from the drilling fluid and quantifying them would enable geologists to determine, as drilling progressed, the quantity and type of fluids contained in the reservoir with great accuracy. The interpretation of gas readings is well documented; however, a number of factors affect the formation fluids during the liberation and detection cycle. Areas of potential loss have been documented, but the most important potential loss have been documented, but the most important factors controlling the levels of gas detected are at the surface: (1) the rig surface system (Fig. 1), (2) the extraction mechanism, and (3) the detection system. This paper examines all three factors and proposes new methods to overcome the problems they present.
|File Size||461 KB||Number of Pages||6|