Acquiring downhole pressure data is essential for successful reservoir management; it paints a picture depicting the reservoir's behavior. Presently, the intelligent field concept has matured to such an extent over the last decade that several major oil operators in the world now have fields where intelligent technologies have been deployed on a large scale. Saudi Aramco is one of the pioneering oil & gas operating companies, which have put huge investment to transform its oil fields into intelligent fields with expectation to maximize the hydrocarbon recovery, simplify operations and minimize human interaction hence enhancing safety. As the concept of intelligent field has matured, more and more operators are embracing this new concept with expectations for higher recovery factors. Permanent Downhole Monitoring Systems (PDHMS) is one such intelligent field component which provides continuous monitoring of reservoir pressure. PDHMS has become indispensable tool for reservoir surveillance particularly for offshore fields in which gauge deployed pressure and temperature surveys are always affected by external factors such as the weather. PDHMS's are installed to eliminate wire-line unit and/or expensive barge visits. Another obvious advantage is that the system can turn any shut-in time as an opportunity for both pressure survey and well testing, thus largely reducing the non-productive time of a producer and significantly improving the reservoir surveillance frequency.

The installations of PDHMS consist of two electronic gauges installed normally at the end of tubing with a distance of some 200 ft to 300 ft of true vertical depth (TVD) between the gauges to profile the gradient. These gauges are connected to surface recording and data transmitting equipment through an electrical cable or fiber optics attached to the outside of well tubing. The installation and retrieval of PDHMS, in case of malfunction requires capital investment in the form of rig utilization. Rigless wireline deployed gauges have been considered in the past but with cable running inside the tubing making it containing more disadvantages than advantages. Hence the next progression of this technology was a wireline retrievable gauge without the need for any cable, cableless pressure gauge allowing a wireless broadcast of data. These battery operated gauges can be set and left in the hole riglessly for an extended period of time of up to three or more years, depending upon data transmitting frequency. This technology was recently trial tested in one of the Saudi Arabian fields for about a year with promising results. The aim of utilizing such system was to improve well intervention safety, control cost, and optimize resources. Additionally, like PDHMS, cableless gauges have a huge potential to simplify logistics compared to conventional surveying. They are superior in the fact that they are wireline/slickline deployed. This further opens the opportunity to replace failed PDHMS with cables-gauges in offshore environment in particular to continue monitoring pressure without waiting for a work over rig resources.

Saudi Aramco's strategy is to further revolutionaries the use of the technology behind cableless gauges by installing them in selected observation wells at the datum point depth if feasible. With this cableless gauge, only one gauge will be required as compared to the conventional practice of installing two PDHMS gauges. This paper will address old and new methods including conventional wireline survey, well testing, PDHMS and cableless gauges, which are utilized to obtain downhole pressure to establish a tangible comparison between them. The paper also discusses a method to estimate the static bottom-hole pressure (SBHP) through extrapolation to datum empirically.

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