No abstract

Wellbore strengthening techniques have been used in recent years to increase the capability of wellbores to maintain higher pressures. By increasing the fracture resistance of formations, operators can save rig-time and large volumes of drilling fluids. The Luna-41 well, offshore Italy, intersects a critical interval comprising high pressurized formations overlaying a lower pressure depleted zone. The initial plan for the well was to divide this interval into two separate hole sections using two different mud systems. A casing string would have been set to isolate the shallower high pressure region followed by an expandable liner to isolate the over pressured shales laying above the depleted reservoir level. An alternative design was proposed that required only one fluid system and a single casing string, thus saving an expandable liner. Thanks to the wellbore strengthening application and the proprietary continuous mud circulation device, the accomplished well program allowed an 8-day rig-time reduction and a 3-MMUSD cost saving. A specific modelling tool developed for wellbore strengthening applications was used to assist with fluid design. The tool calculates the width of microfractures induced by differential pressure and the Particle Size Distribution (PSD) of carbonate materials required to plug such microfractures and ultimately strengthen the wellbore. The mud formulation for Luna-41 was tested in the laboratory using a Pore Plugging Apparatus (PPA) and aloxite discs with pore sizes corresponding to the calculated microfracture width. The fluid used to drill the critical interval was a salt saturated system based on polyglycerol complex and supplemented with a polyamine inhibitor. The field application was a success. The depleted zone was drilled without incurring lost circulation. This paper describes the results of the field application as well as the fluid engineering process and laboratory testing to highlight the benefits - such as accessing depleted reservoirs and saving casing strings - that wellbore strengthening combined with a continuous mud circulation system can bring to the industry.

Hydrothermal alteration is an interaction between rock and hydrothermal fluid by means changing the mineralogical composition of the rock. This process is controlled by permeability, chemical composition, temperature, pressure, and duration of the hydrothermal alteration. Gunung Pancar, located in West Java, is considered an outflow for Gunung Gede Geothermal System. Typical geothermal surface manifestations found around Gunung Pancar are hot springs, warm ground and surface alteration. Basic geological mapping was conducted followed by water and altered rock sampling. Petrographic and diffraction methods are completed to confirm altered protolith. Water analyses were conducted to determine water type and origin. Alteration zonation is then inferred based on the water type, intensity of alteration and then cross referenced with indication of structural geological features. Zonation reveals that the intensity of alteration gets weaker as it moves away from the apparent faults. The result suggested that the permeability of the host rock affects thermal fluid movement around Gunung Pancar and subsequently the local geothermal conceptual model.

This paper highlights how the implementation of an extreme lean casing profile for the well construction, can really make the difference to achieve operational excellence. This is the case of the successful application in a mature field, where, for the first time, the reservoir target has been reached with a horizontal 8½Љ hole section within naturally fractured carbonate formations.In such occasion, the extreme lean profile has made it possible to reach the reservoir with a bigger production hole diameter, compared to the previous wells drilled in the same area; this has allowed the accomplishment of an outstanding production performance, also thanks to the lower pressure losses inside the 8 ½Љ open hole section.The reduced clearance between casing and borehole represents a distinctive characteristic of the extreme lean profile; this enables using two additional casing strings, as a contingency for well construction or as extra casings to reach deeper targets with the same production hole diameter or, as in this case, start with a smaller surface hole while simultaneously reaching the reservoir with a production hole diameter larger than those of conventional wells.Furthermore, the specific well design has allowed to reduce the drilling time, improve borehole stability thanks to the smaller hole sections, and decrease the environmental impact as a result of the reduced volume of cuttings produced.This paper provides a comprehensive description of the well requirements, the associated operational issues, the chosen solutions and the actual challenges encountered during drilling operations. The achieved results are also described.

Banten is an area that has geological uniqueness, particularly in Rawa Danau on the North side. The research area is a young volcanic complex surrounded by several mountains such as Mount Aseupan, Parakasak, and Karang in Serang district in Banten province. The Rawa Danau consists of swamp and lake, which is located inside an estimated Pliocene-Pleistocene caldera as the result of the ancient volcanic eruption. Based on the previous study the lithology of the lake was fine-grained fluvial sediment and swamp deposit with volcanic material. The aim of this study is to reconstruct the behaviour of the eruption in the research area and to know the area affected by the eruption using petrography analysis. The research area is dominated by pyroclastic such as breccia, tuff, and andesite in the form of lava flow and basalt that originate from M. Parakasak, M. Aseupan, and M. Karang. The mineral contents of the igneous rocks are plagioclase, pyroxene, and opaque with the microlith plagioclase as the groundmass. The degree of plagioclase extinction angle was used to differentiate between andesite rock and basalt rock. Andesite rock has more acidic plagioclase than basalt rock. The texture of andesite rock is trachytic implied that the geometry is a lava flow. The basalt rock has porphyritic texture and becomes the part of the caldera wall of Mount Parakasak.