Unconventional Reservoirs Diagnosed by Neutron Sensing Methods
The paper suggests the technology for identification of unconventional oil and gas reservoirs by non-associated gas. Gas escapes due to powerful vibroacoustic impact of drilling tool, as well as alternating pressure arising from tripping. The article also outlines the diagnosis of gas accumulations near wellbore by neutron sensing methods. The impact of non-associated gas increases while measuring immediately after casing and cementing. Best results are obtained when comparing time measurements (by neutron sensing methods) in open hole and immediately after casing and cementing. This is caused by the contraction effect, which is consisted in shrinkage of the set cement compared to when it was in liquid state. Cement shrinkage leads to repression of the reservoir and pulling up a non-associated gas, as the most mobile fluid, to the column with cement stone. This technology allows allocating unconventional reservoir and specifying its lithological composition. The proposed technology is based on different sensitivity of neutron sensing methods to a deficiency of density and hydrogen content. Such technology, when saturation is determined by a deficiency of density and hydrogen content, was tested in wells of Baltic oil and gas province in order to identify oil and gas intervals in shale reservoir. The article shows the first positive results obtained. Though, reliable assessment of geological informative value requires further broader testing of the proposed technology.