Sourceless Well Placement with Real-Time Acoustic Measurements

Abstract

Sourceless well logging (logging without using traditional chemical sources) has become more attractive in certain locations because of evolving government regulatory and HSE requirements. LWD sonic tools provide opportunities to operators for both well placement and formation evaluation. For the first time in the UAE, an LWD acoustic tool was added to a bottomhole assembly (BHA) to acquire sourceless porosity measurements to help stay in the porous sub-layers in the target reservoir. In comparison to more traditional nuclear measurements, LWD sonic has a superior depth of investigation that is less affected by standoff and a driller-friendly BHA free from stabilizers. Based on the evaluation of offset data, which indicated excellent correlation of sonic vs. density/neutron measurements, we decided to provide shear porosity in real time owing to the sequence stratigraphy and corresponding energy partition. A post-job comparison with density/neutron data acquired in a wipe run was also conducted to verify the sensitivity of real-time acoustic porosity measurements for both well-placement and formation-evaluation purposes. Sonic-derived porosities were found to be instrumental in the real-time decision making needed to keep the well the in higher porous sub-layers. Current developments, including real-time azimuthal sonic together with considerations of integrating acoustic and NMR measurements in both petrophysical modeling and field applications, show promise in providing reliable sourceless porosity estimation in these formations. This case history delivered a BHA free from radioactive chemical sources. Safe drilling objectives as well as maximized productivity per unit lateral length were achieved despite the potential risks associated with the faults that were observed in the pilot hole. Introduction With a global focus on exploring oil and gas with minimum environmental impact, the regulations in the region are very strict on adhering to zero harm to the environment. One of the most stringent laws in place is with regards to the abandonment of radioactive sources in the well in the event of a stuck pipe. ADMA OPCO is an active player in helping service companies develop and improve on their “sourceless” alternative technologies to reduce potential risks associated with stuck pipe. Real-time acoustic measurements were used for well-placement purposes in Field A, which is one of the giant fields located in offshore Abu Dhabi. Oil was discovered in 1958, and production began in 1962. Down-flank water injection started in 1973 followed by crestal gas injection in 1994. The Arab reservoir in Field A was formed from regressive cycles of sedimentation divided into four highly heterogeneous sub-reservoirs (labelled in ascending order from A to D (Fig. 1)). The principal oil-producing reservoirs are Arab zone C and Arab zone D, whereas Arab zones A and B still remain undeveloped. Based on the core description, the Arab reservoir section is mainly composed of three lithologies, namely, anhydrite (purple shading), dolomite (green), and limestone (light blue), as shown below in Fig. 1.