WHAT IS A PERMANENT GAUGE SYSTEM?
A permanent downhole measurement system is more than a pressure and temperature sensor;
It is the downhole sensor holder or gauge chuck as some call it, that holds the sensor in place and provides a pressure channel (port) from the production stream.
It is the sensor itself.
It is the cable that goes from the sensor to the wellhead system.
This cable is also sometimes referred to as TEC (tube clad cable) or "flat pack".
Wireline protectors/clamps secure the wireline to the tubing and protect it during well installation. (Some "daredevils" are using metal straps / "metal straps")
These are the cable splices, if used.
These are the packer glands, if used.
These are downhole electrical or fiber optic couplers, if used.
It is the penetration with the electrical coupler or the TEC through the wellhead system.
Is the wellhead outlet assembly.
It is the cable from the wellhead to the data acquisition system, interface card, umbilical, etc.
It is the software system that obtains, converts and transmits the sensor signals.
It is the total system required to detect and bring the data to the desk of the engineer who needs it.
And last, but by no means least: It is the personnel of the preparation and execution of the installation and the labor at the site of the well!
RESEVOIR and DRAINAGE EFFICIENCY MONITORING
Having a downhole pressure and temperature measurement system in your well provides you with real-time data and insight into the reservoir, and steps can be taken to improve reservoir drainage, survey performance, etc.
When such changes are made, the downhole detection system will verify that the action you have decided has the required effect on the drainage of your reservoir. Downhole detection is really about two things; Increase the drainage of your reservoir and save costs by not having to perform downhole intervention studies.
Basically, gauging systems give you better reservoir management leading to higher daily production and total field drainage, better reservoir characterization, better production optimization, better flow allocation, and an in-depth tool. real-time diagnostics for wells. You'll also experience significant cost savings on well testing. By not having a downhole gauge, you are essentially blindfolded.
As stated in SPE article 102700: “Reliability evolution of permanent downhole gauges for subsea wells in the Campos basin: a 10-year case study” (HM Frota & W. Destro, Petrobras ):
“These systems are playing an increasingly important role in improving reservoir and well management.
They are becoming a very important issue in forecasting the future performance of wells and reservoirs.”
Any reservoir and production engineer understands the importance of forecasting; It is simply the reality check for any operating business and an indication of whether or not you will have a job in the coming year.
(The following information has been obtained through experience, from various SPE papers, Oilfield Review, etc.)
Interference Testing where the downhole gauge system establish the degree of communication across the field where such gauge system(s) are installed, between wells, between fault blocks and also the vertical transmissibility between reservoirs.Benefits are that wireline interventions for pressure surveying are eliminated, which lowers risk of loosing tools downhole, chance of personnel injuries, etc. Also, limited planning for survey is involved. Observation of effects are caused by any change in production or injection in wells where permanent gauges are installed.
Reservoir Pressure Control by maintaining bottom hole flowing pressure above a threshold by monitoring permanent gauge data while adjusting water or gas injection, or while varying production.Benefits are that individual well production is maximized, injection rates are optimized, sand production is eliminated by controlling the drawdown, and the completion costs are optimized.
Transient Well Testing is performed automatically be a pressure build-up test whenever a well containing a permanent gauge system is either deliberately or inadvertently shut-in. Similarly a pressure drawdown test is performed when the well is opened up.Benefits from this are that transient analysis of problem wells are performed with minimum intervention, real-time early reservoir data with no cable within the flow-stream are obtained during extended well testing or early production. Also, remote control and analysis of data is possible. Another great benefit is that the production loss are limited by the elimination of wireline survey interventions.
History Matching are easily performed, as the permanent gauge system provides continuous recording of downhole pressure data during the lifetime of the well.Clear benefits are verification or adjustment of reservoir models are possible “on the fly”, system provides data input for improved reservoir description and reserves estimates. Well Performance knowledge are obtained by the continuos recording of downhole pressure data.Benefits from this are that by pressure monitoring downhole, you have the tool to monitor the completion / gravel pack performance. Also, scale build-up in the tubing string can also be detected and monitored.
Well Performance knowledge are obtained by the continuos recording of downhole pressure data. Benefits from this are that by pressure monitoring downhole, you have the tool to monitor the completion / gravel pack performance. Also, scale build-up in the tubing string can also be detected and monitored.
Hydraulic Fracturing is monitored by downhole pressure during the fracturing operations, where benefits are the optimization of fracture length and fracturing efficiency evaluation by bottom hole pressure response.
Bottomhole Pressure Data will also provide information on pore pressure that can be calculated for safety while drilling development wells in the area. This also provides valuable data to select accurate kill fluid weight. The data also can be used to improve accurate under- or over-balance before perforating.
RESTRICTED WELLBORE ACCESS
Also, install a permanent downhole gauge system whenever access is restricted by subsea completion wells, small platforms or single wells, remote land wells or when other activities on a platform such as e.g. continuous drilling, prevent well survey access.This eliminates costs associated with wireline survey interventions, reduces operational hazards, removes the need for personnel on location for pressure survey, does not require a rig and in many cases offers the only method the record downhole data.
Installing a permanent downhole gauge system together with the well completion in highly deviated wells offers the elimination of costs of coiled tubing, snubbing or wireline “tractor” interventions for pressure surveying.
Other:
Reduce ambiguity and uncertainties in the interpretation
Detect the changes in reservoir properties, such as compaction
Monitor skin, permeability and pressure draw down over time
Evaluate the performance of stimulations or workovers
Evaluate completion performance
Identify well problems quickly
Identify reservoir connectivity
Detect drainage area change
Evaluate operational efficiency
Improve flow back time of new wells
Obtain initial build-up data
Assist reservoir simulation and history matching
WELL COMPLETION PUMPING HARDWARE
PERFORMANCE MONITORING
Mounting downhole gauge systems to monitor pressure downhole and combining this with wellhead measurements ensures pump performance improvement, lowers failure rate of downhole pump systems and also provides early warning on possible pump failures.
Now, combining such permanent downhole point pressure- and temperature sensing (where of course several sensors can be placed in a number of locations downhole, all connected to the same cable if required). What is important for DTS is that the system is based on measuring the temperature and monitoring very small changes (less than 0,01 deg. C) to this temperature - Anywhere along the cable. It is the entire cable length that is the sensing media. No sensors are embedded into the cable. To measure, the cable of course has to be placed at the location where data is required, and that normally means that the cable has to go to the very bottom of a wellbore, to the area below the lowermost producing or injection zone.
As commonly known, any changes in a wellbore caused by changes in flow-rates, fluid compositions, leaks, etc., has an effect on the temperature. So being able to detect such a temperature change, we can by combining the sensing with wellbore knowledge and experience interpret what is actually taking place in a wellbore.
Typical values are:
Verify gas lift valve operation in gas lifted oil wells
Verify and tune downhole flow control valves
(“intelligent” completions)
Identify and observe cross flow and fluid movements behind casing
Identify and observer channelling effects between zones
Identify and observe wellbore leakages, including production annulus to tubing leakage, casing and liner leakages, cement integrity, etc.
Observe fluid entry points, gas- or water breakthrough
Observe and quantify zone injections and/or inflow for multi-zone wells, including lateral wells, and create an understanding of changes in this over time
Fracturing efficiency observation (also in tight gas producers), including stimulation placement
Observe steam front•Monitor rat-hole (sump) liquid filling
And many other uses where small temperature and/or pressure changes provides reservoir- and wellbore condition information
