The Basic Research On Element Logging While Drilling Method

Element logging not only can be used to determine the content of elements in the formation,but also be used to identify the lithology of the formation,which has important research significance for the evaluation of unconventional complex lithologic reservoirs.With the activity of high-angle wells and horizontal wells carrying out,it is extremely urgent to study the element logging while drilling.The LWD technology not only can objectively and truly reflect the actual geological characteristics of the formation,but also reduce costs and improve the quality of measurement data.At present,there are no studies on element logging while drilling in China.In this paper,a tool model of element logging while drilling based on ²⁴¹Am-Be neutron source and consisting of a He-3 thermal neutron detector and a LaBr₃ crystal gamma detector is proposed,the mechanism research on element spectrum logging while drilling is carried out by means of numerical simulation.Firstly,the results of the field distribution of neutron and gamma and element spectrum measurements obtaining by drilling instrument and cable instrument were compared,to study the effects of drill collar.In order to improve the measurement accuracy of the element content,the optimization design of the drilling instrument was carried out,including the source distance of neutron detector and gamma detector,the position and thickness of the shield,the position of the boron.The detection characteristics of the tool that has been optimized are studied,including detection depth,vertical resolution and the uncertainty of element yield.Finally,a numerical simulation study was performed on the dual-detector element logging response while drilling,to verify that using spectrum response from gamma detector can accurately determine the element content in the formation,and to study the combination of information which obtained from neutron detector and gamma detector to determine formation porosity and formation water salinity.The tool of element logging while drilling designed and researched in this paper not only can be used for the accurate determination of elemental content,but also for the calculation of formation porosity and formation water salinity.It can break the traditional cable element logging method and promote the development of logging-while-drilling technology.