In a number of my prior applications, op. cit., I describe using a portable NMR instrument so that flow properties of rock samples can be accurately and swiftly measured, especially at remote field locations. The described principle of operation: spin-lattice relaxation times of fluids in chip samples, can be accurately correlated with flow properties of different rock samples.
In a lesser number of my prior applications, op. cit., I describe difficulties of NMR instruments that did not have characteristics of which I based my prior advances: large DC field inhomogeneity and unusual background phase incoherence. I found in a number of applications that at least one of the above-mentioned conditions had been eliminated.
To take into account such instrument variation, in my co-pending application, Ser. No. 255,977, filed Apr. 15, 1981, U.S. Pat. No. 4,412,179, op. cit., I reinserted phasal incoherence into the system. Method of insertion: a gating code was created by a computer-controller for controlling a transmitter-pulser such that RF interrogation is limited in distribution to at least a cycle at the nuclear magnetization precessional frequency. While the above gating code was useful in many circumstances, it is still desirable to have a system that has the capability of more flexible operations, viz., to be useful in field situations irrespective of whether (or not) phasal incoherence is (or is not) inherently present in the field system, yet continue to provide the improved flow-through efficiency of my previous embodiments.