As a part of a research program aiming to mobilize marine gas hydrate deposits as an energy resource, the worlds' first gas production attempt was performed in early 2013 in the Daini Atsumi Knoll, Eastern Nankai Trough, off Honshu Island, Japan.

This paper describes a new method based on the analysis of non-steady state wellbore temperature distributions impacted by geothermal temperature profile, Joule-Thomson and adiabatic effects in reservoir flow to describe near wellbore parameters such as permeability distribution and to estimate flow rate distribution between producing layers. The solution of the inverse problem with respect to parameters of near wellbore zone is based on the quantitative analysis of the transient baro-thermal effects resulting from the single-phase fluid flow from the reservoir into the wellbore. In the steady state case the reservoir thermal effect is the same as the throttling (Joule-Thomson) one. It is reduced to the adiabatic effect while the fluid is stagnant. In the general case for non-steady state flow the change of reservoir fluid temperature is a combination of frictional heating and cooling resulting from the expansion of the fluid. Non-isothermal well testing (NIT) relies on the analysis of these fluid temperature changes. The method discussed in this paper allows evaluating parameters of near wellbore region (permeability and radius of damaged zone) and could be complimentary to the conventional well testing practices for a single-layer reservoir and to estimate flow rate distribution among the pay zones in a multi-layer case (zonal allocation). The paper develops mathematical models and presents the results of numerical simulation for transient processes after the start of the production phase and during well test operations including multi-rate testing. Limited to the particular cases of unsteady processes after specific wellbore operations (changes of production regimes and shut-ins), the transient analytical solutions assume that the fluid may be considered incompressible and that no conductive heat transfer occurs. In order to take into account compressibility and thermal conductivity, detailed numerical modeling has been performed. The paper compares the numerical results to experimental data and shows that the fluid heat capacity in wellbore perforated zone must be considered for appropriate interpretation of initial bottomhole temperature change versus time, in particular for small rates. Based on the analysis of the simulation results, an inverse model solution for the estimation of the near wellbore zone parameters from reservoir fluid temperature and wellbore pressure transients is proposed. The method comprises first-order estimation from analytical solution and their further numerical refinements by non-linear regression for the system "reservoir-wellbore". Example of interpretation of non-isothermal well testing field data is presented demonstrating the usefulness of this new methodology.

Cleanup operations are often challenging to predict. The review of the major physical phenomena governing the behavior of a well cleanup sheds light on some important considerations to be taken to design and realize such operations. An optimal cleanup program will depend on the well construction processes, the lithological factors and the interaction between the drilling fluids and the formation, active sequencing of chokes. The coupling of these complex physical operations can be non-intuitive. A modeling approach is proposed and validated through comparison with field data. The design of an optimal cleanup program is hampered coupling of two issues: the existence of formation damage due to the invasion of mud in the near well-bore area and the transient well bore phenomena associated with the replacement of drilling or completion fluid with lighter hydrocarbons. This paper investigates the integration of transient simulation of near wellbore multiphase phenomena with complex wellbore dynamics and provides recommendation on cleanup designs. The success of a wellbore cleanup is gauged in different ways, depending on the lithological, drilling and operational environments. Metrics of performance such as duration of the operation, productivity, recovery of loss fluids are commonly used. We tackle the global issue with a predictive model specifically tailored to cleanup operations in a layered system that considers: An internal mud cake (which is formed by mud solids intrusion into the formation) An external mud cake (formed at the interface well / formation) A mud filtrate invaded zone Potential perforations Dynamics of the multiphase (and multi-component) wellbore flow Flow control devices The paper discusses the laboratory validation of the near well bore model against dynamic core flooding and transient return permeability experiments. Comparisons against field data obtained with high speed multiphase flowmeter or dynamic production profiles further enhance confidence in the simulations. A number of recommendations for cleanup designs are provided considering some of the challenging constraints such as: Operational constraints: limited storage volume, rig time, pressure drawdown limits (collapse), noise, rates Fluids limitations: avoiding drawing pressure below bubble / dew points Geomechanics limitations: max drawdown or avoiding tubing collapse or protecting other completion elements such as screens Lithological challenges: multilayer reservoirs and horizontal wells where it is necessary to clean all layers / drain. Large drilling losses resulting in perforation channels not bypassing totally the mud filtrate invasion zone (and sometimes the internal mud cake area) The analysis of the sensitivity of various model parameters confirms the need for robust cleanup designs that takes into account the actual uncertainties of the well construction process and of the formation heterogeneities and near wellbore characteristics. This study demonstrates that the principal cleanup characteristics are essentially dependent on properties of the drilling and completion fluids. It is possible to give some practical operational recommendations for improved cleanup such as zone selectivity, choke sequencing and pressure controls. The utilization of temperature variations at the on-set of the cleanup also provides important knowledge to the interaction of the drilling fluids and completion fluids with the formation prior to the test. This information can be used to optimize the next well. The monitoring in real-time (or in-time) of the downhole parameters such as pressure, temperature can significantly help to reduce the uncertainty of the cleanup operation and decrease substantially the rig time.

Permanently installed monitoring-sensor cables behind the production-well casings were used to acquire distributed-temperature data, and electrical potentials were passively monitored at the down-hole electrodes in the winters of 2007 and 2008 for the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Research Well Program. The data could be almost continuously acquired during the production-test periods without interfering with production operations once the down-hole-sensor cables were connected to the surface system. Some useful information related to production activities was obtained from the distributed-temperature data. The temperature-depth profiles obtained during the depressurizations in the 2008 test indicated a promising potential for tracking of the fluid levels in the annulus, which qualitatively corresponds to the fluid-volume change estimated from the differential pres-sures. Temperature profiles also contributed a complementary estimation of production parameters, such as the water-production rate under assumed conditions. The temperature disturbance observed during cement curing suggests a thermal impact on the gas hydrate by the heat of cement hydration. Passive electrical-potential measurement is considered a promising candidate for further development. The measurement was attempted to acquire streaming-potential signals from formation-fluid movement in porous media under the pressure gradient during various operations. Qualitative observation shows a rela-tionship between signal-polarity change and the direction of possible fluid flows in the formation, which suggests local-scale fluid flow near the electrodes.

Quality of well testing in highly productive reservoirs directly depends on the pressure-gauge placement in the wellbore. This paper documents the impact of the placement of downhole gauges on pressure transient analysis (PTA) for high-productivity reservoirs. The article illustrates cases where this latetransient behavior is strongly influenced by temperature effects, which can lead to significant errors if not considered during the interpretation process.Although the correction of measured pressure to datum is possible by proper modeling of the influence of non-isothermal effects on the test string and the produced fluids caused by temperature changes, it is preferable to avoid this situation by suitable gauge placement. This greatly facilitates a more accurate interpretation of data using PTA with a reduced uncertainty in the definition of the appropriate reservoir model to use. Proper modeling during the test design of these temperature effects on the correction of pressure to datum also allows the determination of the resulting uncertainty pressure variations and the selection of the optimal test-string design, with consideration made to the expected temperature changes, fluid present in the wellbore, and range of productivity. Reconstruction of pressure is also possible despite a high level of resulting uncertainty.A workflow for reconstruction of pressure data taking into account temperature effects is proposed. We emphasize that such corrections cannot substitute the correct pressure measurement for successful well-test data interpretation. Present gauge technology allows proper test design and correct placement of pressure and temperature gauges in close vicinity of the interval of interest, to avoid or minimize potential problems related to the reconstruction of the measured pressure to datum.