|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Bukovac, Tomislav (Schlumberger) | Belhaouas, Rafik (Schlumberger) | Perez, Daniel Rafael (Schlumberger) | Dragomir, Alexandru (Petrom SA) | Ghita, Viorel (Petrom SA) | Webel, Carlos Emilio (Schlumberger)
Abstract Offshore operations are extremely expensive because of the operational environment and the necessary infrastructure. In this environment, emphasis is placed on high-efficiency operations based on specially tailored solutions combining available resources with new technologies. This results in a significant impact on operational efficiency by lowering costs and ultimately increasing hydrocarbon production. To introduce greater efficiencies in offshore operations, a horizontal openhole candidate well was selected to be equipped with a permanent completion system that would enable multiple fracturing treatments. Later, it was determined that by using a novel viscoelastic polymer-free surfactant-based fluid, the entire operation could be performed in a single operation, adding additional savings to the process and improving efficiency. Interpreted openhole images and advanced sonic logs were used to determine the optimum completion configuration and to select favorable fracture initiation points and treatment designs. Because a specialized fracturing vessel tailored for operations in the Black Sea was not available, a supply vessel was used. The vessel had all required fracturing equipment rigged up and secured on decks. To enable sufficient fracturing fluid volume for placing three propped fracturing treatments in a single pumping operation, a polymer-free fracturing fluid was formulated and mixed with seawater continuously. This novel multistage fracturing system was introduced in Europe for the first time. Results indicate a sustained increased production. Because of this success, additional wells are scheduled to be stimulated using same approach in the following months. Introduction The Lebada Vest field is situated ~95 km offshore Romania in the Black Sea. This field was discovered in 1984 and put on production in 1993. Since then, numerous vertical oil and gas wells were drilled and completed (Fig. 1). The wells were produced initially in natural flow and later equipped with gas lift to enhance ultimate hydrocarbon recovery. The target reservoir is a Cretaceous-age formation located at depths of ~1,900-m true vertical depth (TVD) composed of varying shale, sandstone, and carbonate content. The laminated pay zone is generally formed by streaks with permeability ranging from 0.1 md to 2.0 md and average of 0.8 md. Reservoir rock porosity ranges between 15% and 22%. Bottomhole static pressure (BHSP) at ~1,850 m true vertical depth sub sea (TVDSS) sub sea is ~220 bars and bottom hole static temperature (BHST) is 93°C.
Medina, Maximiliano (Helix RDS Ltd.) | Morantes, Giovanny (Petroleos de Venezuela S.A.) | Morales, Jhonles (PDVSA) | Guevara, Wilton (Schlumberger) | Romero, Jorge Alberto (Schlumberger) | Gonzalez, Yosmar J. (Schlumberger)
Abstract Located in Eastern Venezuela the Santa Ana Field is part of the most important gas province of Venezuela: Anaco District. Its main productive zones are the Merecure and San Juan formations, which are sandstones characterized by their high permeabilities (100 - 500 md) and low pressures (1200 - 2200 psi). The wells in Anaco District are normally perforated using conventional static underbalanced techniques. The productivity of these wells was evaluated using nodal analysis techniques coupled with perforating performance simulations. The quality and amount of data was recognized to be limited. However, a qualitative diagnosis of these results indicated that the static underbalanced condition and the shaped charges used were not enough to effectively clean the perforation tunnel and surpass the near wellbore damaged zone. Dynamic underbalanced perforating coupled with high performance charges was selected as the technology that would improve productivity in the challenging wells of Santa Ana. This technology has been applied in similar scenarios across the industry in recent years, although no documentation was found on its use in such low pressure environments. This paper describes how dynamic underbalanced perforating was deployed successfully, while pushing the limits of its application envelope. To obtain a dynamic underbalanced condition in such a low pressure environment, the shot density had to be reduced to 2.5 spf, raising concerns about its effect on well productivity. Two wells were selected for this field trial. They were perforated using a TCP/DST string, which allowed the well to be tested immediately after perforating. Details of the diagnosis, planning, execution and evaluation phases of this project are described. The resulting gas production and zero perforation skin represented more than a two-fold productivity increase compared with the target reservoir average well production. These results demonstrate the effectiveness of the technique under borderline conditions, and promote its application in similar scenarios worldwide. This project shows the importance of production and perforating diagnosis, leveraging technology application and pushing the limit of dynamic underbalanced perforating in order to increase productivity in mature/low pressure assets. Introduction Perforating can be defined as the process of connecting the well with the reservoir by creating a tunnel which goes through the casing, cement sheath and the reservoir rock. The main objective of perforating is to create a clean tunnel sufficiently long that it reaches the undamaged reservoir. This process is fundamental to the productivity of the well; however, its importance is often overlooked during completion operations. It was recognized that perforating was an area that could be improved in Anaco District well completions. As a result, a qualitative evaluation of conventional perforating performance was done. This evaluation confirmed the link between poor well productivity and perforating and justified the field trials of new technology in this area. Most of the perforating technology developments have been focused on obtaining deeper penetrations. However, few breakthrough advances have been achieved relating to tunnel quality. The industry has relied solely on static underbalance, which is now a well recognized technique for perforation cleanup. The appropriate level of static underbalance has been extensively researched; however, more recent investigations have presented relevant evidence indicating that static underbalance is not the only governing factor in effective perforation cleanup.
Abstract The Lebada East oilfield - of the Upper Cretaceous formation on the Romanian Continental Shelf of the Black Sea, located at a depth of 2,100 m, is a microfractured type reservoir, with a matrix permeability in the order of tenths of milidarcies and with an equivalent matrix-fractures effective permeability with values comprised between 0.5 and 1.5 mD. The production tests of geological investigation wells have proved that this reservoir can be commercially produced by vertical wells only after performance of some hydraulic fracturing operations in view of obtaining large dimensions fractures, which are operations based on expensive, advanced technologies. In 1993, on this reservoir, the first horizontal well in Romania (Well LO1-Lebada East) was designed, drilled and brought in. The horizontal drilled length of Well LO1 is 650 m. The geophysical investigation logs carried out during drilling point out that only 250–350 m of the drilled length are porous-permeable. The well was completed with a 7 in EL liner, slotted over a length of 588 m. Well rocking to production required stimulation treatments. The efficiency of these new technologies on oil reservoirs with low effective permeabilities - that cannot be profitably produced with vertical wells - has thus been proved. The favorable horizontal well performance opens the prospect of reserves recovery from this productive formation. Introduction Horizontal drilling started to be applied in our country in 1993, when the first offshore well, LO1 - Lebada East, was drilled. The LO1 - Lebada East well started the development of the oil reservoir from the Upper Cretaceous on the Continental Platform of the Black Sea, a reservoir which is at an average depth of 2,100 m. The reservoir is characterized by low effective permeabilities, whose production by vertical wells is not efficient and results in a very low recovery. The reservoir is microfracturated (with a matrix permeability obtained during the production tests of the geological exploration wells). The production tests of the geological exploration wells led to the conclusion that this reservoir can be produced on a commercial scale by conventional wells only following the performance of some hydraulic fracturing aimed at achieving large sized fractures. These hydraulic fracturing operations are very expensive and their technique and technology are not available in Romanian oil industry. No significant difficulties were encountered during the LO1 horizontal well drilling and there were no significant differences between the designed and the achieved trajectory of the wellbore. The objective for the LO1 - Lebada East well was the production of the hydrocarbons located in the Upper Cretaceous (Santonian + Coniacian + Turonian) formations. Drilling and completion The completion program and the main trajectory elements are presented in Fig. 1. For the LO1 well drilling the designed drilling fluids were used, namely:–over the 150 – 1,281 m measurement depth (MD) interval, a seawater based fluid treated with encapsulation polymers, having a maximum density of a 1,250 kg/m3; –over the 1,281–1,758 m MD interval, an "INHIB-KCl" type fluid, having a maximum density of 1,550 kg/m3; –over the 1,758–3,172 m MD an "INHIB-KCl" type fluid, having a maximum density of 1,350 kg/m3. P. 799