Abstract A supersequence-scale stratigraphic framework is developed for the super-giant Tengiz field of western Kazakhstan through the integrated interpretation of seismic, core, log, and biostratigraphic data. Tengiz produces oilfrom an isolated carbonate platform (areal extent of 580 km 2 ) of Devonian and Carboniferous age. An initial broad Late Devonian platform exhibits vertical growth and was followed by punctuated backsteps during theEarly Carboniferous (Tournaisian and Viséan). The uppermost lower Carboniferous (Serpukhovian) is characterized by several kilometers of platform progradation seaward of the late Viséan platform break. The basal upper Carboniferous (Bashkirian) platform succession was aggradational. Drowning in theearly Bashkirian haltedcarbonate platform growth. Paleotopographic relief on the top of the Bashkirian platformto the basin floor approaches 1,500 meters within several kilometers lateral distance. The stratigraphic architecture defined in this study is used to subdivide the reservoir. The reservoir is also partitioned on the basis of geographic position along a platform-to-basin profile. Time-slice mapping of synchronous depositional facies provides the basis for predicting reservoir distribution and continuity. On the platform, hydrocarbons are produced from Upper Viséan, Serpukhovian, and Bashkirian reservoirs in grainstone and mud-lean packstone lithofacies of the shallow platform and in packstone lithofacies of the deeper platform. Multiple pore types are recognized in Tengiz, but matrix permeability is controlled mainly by intergranular porosity. In-place, upper-slope microbial boundstone and transported lower-slope boundstone debris forms thick and areally extensive mappable reservoirs (Upper Viséan and Serpukhovian) that have distinctive seismic facies and production characteristics. Fractures contribute to non-matrix permeability in these boundstones.

Abstract We present here the results of open-path Fourier transform infrared (FTIR) spectroscopy of gases emitted from the lava dome of Soufrière Hills Volcano. Although measurement campaigns have been discontinuous, they do span a three-year period and provide strong evidence of secular change in the HCl/SO 2 molar ratio from ≥5 in 1996 to <0.5 in 1999. The post-1996 spectral data represent the only available measurements of gas ratios for the volcano’s summit emissions, and complement SO 2 emission rate data obtained by ultraviolet correlation spectroscopy (COSPEC), enhancing the interpretation of degassing at the volcano. The long-term decreasing HCl/SO 2 ratio accompanied an increasing SO 2 emission rate, and suggests a transition from degassing of andesitic to basaltic magma, or progressive tapping of a sulphur-rich vapour phase that was introduced by mafic magma, or that was already resident within the andesite magma reservoir. On timescales of minutes to hours, we observed variations in HCl/SO 2 ratios associated with dome collapses. On 27 July 1998, for example, the HCl/SO 2 ratio dropped from about 0.7 to 0.4 within minutes of a minor dome collapse. A much larger collapse event on 26 October 1998 was followed by a decrease in HCl/SO 2 from 0.6 to 0.1, some 14 hours later. These changes are suggestive of transient degassing from a sulphur-rich source region–larger collapses resulted in tapping of deeper sources, with exsolved gases taking longer to reach the surface. The sustained degassing and response to dome collapse events suggest a permeable upper conduit system established by syneruptive vesiculation, and efficient transfer of volatiles out of the magma chamber by degassing-driven convection in the lower part of the central conduit. Open-path FTIR spectroscopy represents a means for remote geochemical surveillance when access to vent regions is restricted for safety reasons, yielding valuable insights into degassing mechanisms.