EFFECT OF SODIUM CHLORIDE CONCENTRATION IN SAND BED AND WELL ON THE INDICATION OF NEUTRON LOGGING INSTRUMENTS

Abstract

The requirements to the accuracy and reliability of the results of borehole geophysical measurements of the porosity coefficient in oil and gas fields are constantly increasing. Studies of the influence of chlorine on the readings of neutron logging equipment with different types of probes were carried out by mathematical modeling methods. Experimental evaluation of the simultaneous effect of sodium chloride concentration in the reservoir and in the well on the readings of neutron devices has not been carried out. A design description of the experimental bulk model of a porous watersaturated sand formation (a standard sample composition and properties of sand rock) crossed by a well created to study the effect of sodium chloride concentration in the formation and in the well on the readings of neutron logging equipment with various probes, as well as the results of metrological studies of the created model are given. A feature of the model design is the well simulator, made in the form of a cylindrical fiberglass cup and installed coaxially in a cylindrical stainless steel housing. The carriers of the model properties carriers are quartz gravel and an aqueous solution of sodium chloride (NaCl) in its pore space. Reproducible values of porosity model taking into account heterogeneity of crushed stone backfill (0.353 ± 0.002) with probability 1 defined by volumetric and gravimetric methods under normal conditions, the sandy layer, pore space which is filled with fresh drinking water. The results of experimental studies of the effect of aqueous NaCl solution in a sand formation and in a well with concentrations of 50, 100, 150 and 200 g/l on the indication of neutron logging equipment PRKL with probe NGK, RK5-76 with probe NNK-T and SRK-1 with probe NNKNT using individual calibration functions (CF). CF were built on the porosity standards of sandy water-saturated rocks with zero NaCl concentration in the Center of metrological research «Ural-Geo». Correction functions (CF) are given as a dependence of the correction to the readings of the equipment RK5-76 and PRKL on the concentration of NaCl in the formation at a fixed concentration in the well or on the concentration of NaCl in the well at a fixed concentration in the formation. The obtained results can be used in the development of techniques for performing downhole geophysical measurements of the porosity coefficient of rock formations in typical geological and technical conditions.