The dual-burst thermal-neutron-decay-time (TDT™) tool brings two enhancements to pulsed-neutron capture logging. The first is a realistic physical model of pulsed neutron decay curves that accounts explicitly for the effects of neutron diffusion and decay in both the wellbore and the formation. The second is the dual-burst system itself, which permits excellent statistical precision with minimal dead-time losses. This paper discusses the physics of the model, operation of the tool, important mathematical considerations for optimum use of the tool, and a demonstration of the tool performance in a laboratory simulation of a log-inject-log (LIL) operation.
Guest editorial The digital age has dawned. When it comes to information technology (IT), many think the oil and gas industry has been slow to seize the day. But the truth is we embraced IT early on, beginning in the 1950s with reservoir simulation. Since then we have researched, developed, and deployed many additional technologies and applications, with most recent efforts toward full realization of the digital oilfield. Although we have made progress, our industry is at a crucial juncture and needs more than incremental steps; we need a major transformation. It is time to take a deep breath and take the plunge into total emersion, to be like fish in water. Computing technology is no longer the question; it is here and progressing faster than you can say "real-time data transmission and communication." Now we need people with the right skills and vision to use the technology to transform our work. We need digital petroleum engineers. This editorial defines a digital petroleum engineer in the energy industry, describes some roles for the digital petroleum engineer, explains why such a profession is necessary, and lays out the challenge for industry, academia, and SPE for making the profession a reality—now. As the Chairperson of the SPE Information Technology Technical Section (ITTS), I have the honor of authoring this editorial. However, the ideas are based on many discussions over the years with many esteemed colleagues, especially those quoted below who are either members of the ITTS or advisers to the group. They have contributed significantly to the discussion and this editorial. Who is a Digital Petroleum Engineer? In the early days of industry software development, oil and gas professionals were teamed with IT professionals. While we have had some success with this approach, our industry also has a reputation for slow technology uptake. IT is an integrative technology, so it only makes sense to take advantage of this catalyst and develop new roles around it. Because we can link systems from the different disciplines, the technology itself helps to transform the work processes and break down the traditional silos that emerged when, before IT, we had to break down complex problems into their smaller component pieces to solve them. Now IT is allowing us to integrate those smaller pieces together so that we can analyze, optimize, and resolve the whole. At the very basic level a digital petroleum engineer combines IT knowledge with oil and gas content. Of course, we have many people in the industry now who have both of these skill sets. But the bottom line is we need more—many more—and we need them now. We also need to clearly define the skills required to be a digital petroleum engineer, how a person can acquire those skills, the roles they can play in the industry, and a clear career path and opportunities.
The Dual-Burst TDT* (TDT-P) tool is a 1 i!-in. diameter pulsed neutron, dual detector tool system that uses a new method of analyzing the decay of a burst of fast neutrons in the downhole environment. The method provides an accurate measurement of the neutron capture cross section of the formation by employing a physically realistic model of the decay, which accounts for neutron diffusion effects, rather than displaying the de.. cay as a sum of exponentials from the formation and borehole. Intrinsic sigma is computed directly from the decay curve instead of by using correction charts. The model is evaluated using over 2,500 data obtained in well characterized laboratory test formations. The benefit of the method is that the formation cross section is independent of the fluid in the borehole as well as independent of the neutron diffusion characteristics of the formation, characteristics which vary with ~thology.Selected results over the data base are discussed and compared to the results of a two-exponential processing over the same data. The insensitivity of the formation capture cross-section determination with the diffusion model to variations in borehole characteristics as well as tool geometry and, more importantly, timing is demonstrated.Middle-Eastern log results are presented; they include TDT -P versus TDT -M comparisons, showing the variable effect of diffusion for different cases; an example of the insensitivity of formation sigma to borehole fluid • Patent Pending and Mark of Schlumberger 223 characteristics. Results from a two component (formation and borehole) diffusion processing to invert the data, featuring a level by level fit of the diffusion coefficients to the measured data, are presented and compared with the results from a fast, real-time, wellsite computation using a single component model and diffusion coefficients predetermined from external input of lithology and borehole geometry.
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