FRACTURE RESERVOIR CHARACTERIZATION BY FIBER-OPTIC DISTRIBUTED TEMPERATURE LOG
One of the important features of the fiber-optic distributed temperature log is its ability to acquire continuous, instantaneous and simultaneous temperature profile along the entire wellbore. Series of successive temperature profiles sampled every one minute or so enable to analyze transient temperature phenomena, which may pertain to important reservoir properties. For example, when change of rate occurred to the fluid flow such as due to water injection, the temperature profile over the section exhibits transient phenomena associated with the fluid flow. The characteristics of the phenomena depend on several factors including the flow profile which itself exhibits transient nature depending on fluid compressibility, permeability and reservoir extent, the original temperature profile, the temperature of injected fluid and that of the reservoir fluid flowing into the wellbore, the degree of rate alteration, well geometry, flow regime and etc.
Determination of transport properties from flowing fluid temperature logging in unsaturated fractured rocks: Theory and semi‐analytical solution
Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flowing fractures. We argue that FFTL, backed up by data from high‐precision distributed temperature sensors, can be a useful tool in locating flowing fractures and in estimating the transport properties of unsaturated fractured rocks. We have developed the theoretical background needed to analyze data from FFTL. In this article, we present a simplified conceptualization of FFTL in unsaturated fractured rock and develop a semi‐analytical solution for spatial and temporal variations of pressure and temperature inside a borehole in response to an applied perturbation (pumping of air from the borehole). We compare the semi‐analytical solution with predictions from the TOUGH2 numerical simulator. On the basis of the semi‐analytical solution, we propose a method to estimate the permeability of the fracture continuum surrounding the borehole. Using this proposed method, we estimated the effective fracture continuum permeability of the unsaturated rock hosting the Drift Scale Test (DST) at Yucca Mountain, Nevada. Our estimate compares well with previous independent estimates for fracture permeability of the DST host rock. The conceptual model of FFTL presented in this article is based on the assumptions of single‐phase flow, convection‐only heat transfer, and negligible change in system state of the rock formation. In a sequel article, we extend the conceptual model to evaluate some of these assumptions. In that paper, we also perform inverse modeling of FFTL data to estimate, in addition to permeability, other transport parameters (such as porosity and thermal conductivity) of unsaturated fractured rocks.
Hydroxyl production in optical fibres coated with hydrogen-free plastic materials
Optical loss increase characteristics with heat treatment are investigated for two kinds of GeO2-doped silica fibres. The two fibres are coated with polypropylene (PP) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), respectively. Loss increase due to OH ions occurs through heat treatment for the two kinds of fibres below 500°C, although the thermoplastic materials (PP and FEP) generate no hydrogen gas. It is concluded from the experiments that some origin of hydrogen exists in the fibre glass.