Abstract Integrative gravity and structural modelling of Ordovician-Silurian granitoids in the Eastern Lachlan Fold Belt (southeastern Australia) revealed contrasts in emplacement mode and deformation style between coeval S- and I-type granites. The NNE-SSW directed contraction during the Benambran event of the Lachlan Orogen caused dextral movement along two major strike-slip faults (Carcoar Fault/Copperhannia Thrust) and simultaneous formation of both transtensional pull-apart and transpressional shear zones. The geometry and deformation style of the plutons and country rock, their spatial relationship at depth to adjacent faults and the structural history of both the granites and country rocks suggest a genetic linkage between magma emplacement and synmagmatic deformation. Synchronously, the Carcoar Granodiorite was emplaced into a transtensional pull-apart structure and the Barry Granodiorite and Sunset Hills Granite intruded transpressional shear zones. The I-type Carcoar and Barry granites are square to tabular, wedge-shaped bodies exhibiting a weak deformation; whereas the S-type Sunset Hills Granite is an elongated, tabular to sheet-like pluton showing a moderate deformation degree. The contrasts in 3D shape, emplacement mode and deformation style between the I- and S-type granites are due to differences in nearfield stress regime, geometry of the emplacement sites, intrusion level with respect to thermal and rheological conditions, and in their response to deformation. This response is in part controlled by the proportion of resistant/non-resistant minerals in the granite and host rock. This study demonstrates that distinctive emplacement modes can operate simultaneously in different parts of a fault system under contrasting deformation conditions.

Abstract Coalbed methane wells require stimulation, or special completion techniques, to effectively connect the wellbore to the reservoir. A variety of completions and stimulations have been tried, and these are summarized through the end of 1991 as follows (with emphasis on San Juan and Black Warrior basins): Openhole cavity . This has worked best in the "fairway" zone of the San Juan basin where reservoir pressure and permeability are high. The wells can be prolific producers, up to 10 million cubic feet of gas per day (MMCFGD). The cavitation technique is discussed. The physical mechanisms involved in the completion are examined and used to try to understand why cavity completions outperform gel fracture stimulations in gas production in the fairway. Gel fracture treatments . These stimulations are conducted through casing perforations in coal seams. High fracture conductivities are achieved by using 12/20 mesh sand to concentrations of 10 ppg. Although gel damage to the coal formation is evident, moderate productivity increases have been achieved. Water fracture treatments . Because of gel damage to the formation, fracturing treatments have been conducted using water as fracture fluid, plus 12/20 sand to concentrations of a few ppg. In some parts of both basins gas production is greater than offset wells with gel fracture treatments, and the water fractures are cheaper by half. Sandless water fracture treatments . In the Black Warrior basin, water fracture treatments have been performed without sand, using ball sealers to open up more seams. Although their gas production may not

ABSTRACT The Fortescue field is the last of the "giant" oil fields discovered to date in the offshore Gippsland basin, southeastern Australia. This field is a stratigraphic oil accumulation on the western flank of the giant Halibut-Cobia oil field. The Fortescue field discovery well, West Halibut-1, was drilled in 1978—some 11 years after the Halibut discovery—as a follow-up to the dry Fortescue-1 wildcat. The occurrence of a stratigraphic trap in a sand-prone section is a unique feature of the Fortescue field. Fortescue reservoirs are Eocene sandstones that are interpreted as having been deposited in coastal plain, upper shoreface, and lower shoreface environments. Fortescue reservoirs are stratigraphically younger than, and hydraulically separated from, those in the underlying Halibut-Cobia field. Pressure data have conclusively demonstrated that there are at least three separate hydraulic systems within Fortescue field. Reserves are estimated at 280 MMSTB on the basis of an original oil in place estimate of 415 MMSTB. Fortescue field was developed by two 21-conductor platforms, Fortescue A and Cobia A, which also developed the underlying Cobia reserves. These platforms were commissioned in 1983. At the conclusion of development drilling in early 1986, 28 productive wells had been drilled into the field. Peak production of 100,000 BOPD from the combined development facilities was achieved in 1984 and sustained until 1986. Production received a boost in 1989 from two infill wells that were drilled following interpretation of the available reservoir data. Following these successes, a 3D seismic survey was acquired over Fortescue, Halibut-Cobia, and Mackerel fields in 1990. A revised detailed reservoir description based on these data is expected to allow identification of additional infill and workover opportunities and to help mitigate production declines in these mature fields.

Abstract Perhaps no other endeavor undertaken by geologists presents the challenge that accompanies analyses of the fate and effects of wastes discharged into the terrestrial and marine environments. Not only are geological disciplines called into play, but social, political, international, and emotional factors impinge upon the assessment of disposal options and the decisions leading to site selection and disposal operations. There is justifiable concern surrounding the assessment of waste disposal practices. As a recent report by the National Research Council (1986, p. 40) states: Anthropogenic changes in the planetary environment are a unique feature in that they may well exceed the limits of natural regulation. There are many indications that human-induced changes are substantive enough to affect the survival of other organisms, both directly and indirectly, and to pose a threat to mankind itself. Within the Atlantic continental margin, a wide variety of waste-disposal methods are practiced by the industrial, municipal, state, and federal communities. The complexity in dealing with waste-management practices is not confined to scientific uncertainty regarding the behavior of wastes in alluvium (soil), rock, the atmosphere, or nearshore to abyssal sea-floor substrates and water masses, but to a large degree it may be attributed to conflicting regulations, policies, permit requirements, and licenses— all controlled by authorities whose jurisdictions may overlap.

Abstract Man's activities on the continental slopes of the world do not begin to approach the intensity and magnitude of his efforts on continental shelves, yet increasingly we find exploration and development strategies focused upon areas beyond the shelf-break. The primary activity at present involves the search for hydrocarbons, and plans for drilling slope provinces now include sites in water depths in excess of 1500 m. Non-petroleum resources may include old placers, but a greater potential lies in the authigenic minerals which may contain useful elements. Deep-sea benthic fisheries are now under consideration, and advances in trawling and trapping devices may promote a new direction in commercial activity off the shelf. Our exploitation of shelf resources must take into account the impacts and hazards attendant to operating within a dynamic environment. Gravity transport of large volumes of surficial slope sediments is now considered commmonplace, and for activities which rely upon the sea floor for support of structures, pipelines, cables, and other objects the rates and scales of local to regional movements must be understood.