Since the 1950s, there have been two methods used to measure downhole pressures utilizing wireline service technology. The first method is based on the use of a logging cable, and is referred to as surface read out (SRO). The second method, which is more economical and more common, uses slickline and is called (MRO).
Surface Read Out (SRO)
Before the well test begins, high precision electronic pressure recorders are inserted into the well on the end of a logging cable and positioned close to the reservoir of interest. The pressure recorders send their pressure readings to the surface using the insulated conductor in the logging cable. At surface, the readings are displayed and recorded. The logging unit operators and the well test operators continuously monitor the pressure readings for the duration of the test. Vigilant and constant monitoring of reservoir pressures during the test allow for test timing decisions to be made on the basis of reservoir pressure information. This method provides a degree of certainty that the well test will be of suficcient duration to secure the required reservoir information while not unnecessarily delaying commercial production of the well.
Memory Recorders (MRO)
RTM's KC2 tool is one of these memory recorders. Prior to commencing the well test, battery-powered downhole electronic memory pressure recorders are installed in the well using slickline. The recorders are generally left in the well withing about 30 metres of the reservoir of interest. Once the recorders are installed in the well, the slickline unit and crew leave the well site. Unlike SRO (and SDO), there is no connection between the recorders and surface. The battery powered downhole recorders measure and store time-stamped pressure readings in electronic memory, according to a pre-set program. Upon completion of the test, the slickline unit returns to the well site to retrieve the recorders. Once retrieved from the well, the pressure information stored in memory is downloaded to a computer and forwarded to reservoir engineers for analysis.
Smart Drop Off (SDO)
RTM's proprietary Smart Drop Off (SDO) system offers the benefits of SRO testing at a cost that is much closer to that of memory recorders. RTM's system provides the customer with a real time data link between the downhole pressure instrument and a secure internet data port. The use of the latest in materials, electronics and communications technologies has also eliminated the need to maintain personnel and expensive equipment at the well site to support the service. The SDO system consists of an electronic pressure gauge placed at the reservoir, suspended on the end of a custom designed, conductive cable that transmits signals from the downhole tool to surface in real time, at intervals as often as every three seconds. The data from the instruments is available to anyone who is enabled to access it through RTM's secure website. SDO has the capacity to operate reliably under the well conditions encountered in most oil and gas wells.
In addition to the primary downhole pressure measurement, the SDO also measures downhole temperature and can measure surface production tubing pressure, surface casing annulus pressure and ambient temperature. All measured data is handled and made internet-accessible in graphical and text formatted files.
The field equipment required to provide SDO services is packaged in a convenient, all-weather, self-sufficient, autonomously operating unit. The unit is mounted either on a trailer and towed to the jobsite or on skids mounted on a trailer and deployed by a hydraulic crane unit. A heli-portable unit is also in service. The SDO's design eliminates the need to maintain personnel at the well site beyond installation and removal, and minimizes the amount of equipment required, reducing capital costs. The savings are passed on to the customer to create an economically-effective package.
The SDO is a new tool that offers oil and natural gas well operators a re-engineered well testing process. The linking of a sub-surface pressure recorder to the reservoir engineer's computer in the customer's office creates a continuous feedback loop of information. It provides the reservoir engineer with immediate test results, allowing the engineer to adjust the well's flow rate in mid-test, and select optimum timing for shutting the well in and terminating the test.
Precise test timing saves money. Although the MRO method is less expensive than the SDO, the savings are offset significantly when the cost of incorrect test timing is account for. The SDO makes the traditional, expensive SRO method obsolete. Using the SDO, a well that was shut in for a test can be put back on production as soon as the test objectives are met. Usually this translates into an earlier resumption of cash flow for the well operator.
