An integrated analysis of gravity and well data for deep-seated structural interpretation: a case study, from Ras Budran oil field, Gulf of Suez, Egypt

Abstract

Abstract A combined gravity and well-logging data study was put forward to explore the subsurface structural configurations in Ras Budran oil field area. At first, all available open-hole logging data in the form of porosity tools (density, sonic, and neutron), gamma-ray and resistivity logs (shallow and deep) beside the composite logs were used in determining the lithology and dividing it into three different groups, namely, pre-evaporites, evaporites, and post-evaporites. In addition, the Bouguer anomaly map had been integrated with the available borehole information for interpreting the deep-seated structures which not imaged by surface seismic reflection data. The structural analysis is based essentially on the strip off technique to minimize the ambiguity in the deep gravity data interpretation. This was accomplished through computing the gravity effect of each sedimentary layer of a known density and geometry. Several stages of deep gravity interpretation were done by calculating and removing the gravity effect of the overlying sedimentary section above the stripping datum. The process led to localization and enhancement of the gravity anomalies which give more details about the deep structures/sources. In general, the study reveals that the negative gravity effect of the thick surficial layer (post-evaporite sediments) over all the area is strong enough and superior. The positive gravity effect of the shallow evaporites seriously distorts the negative ones of the pre-Miocene clastics. The gravity effect of the deep sources including the Rudeis–Nubian interval generates the most relevant contribution to the strip off gravity, especially in the southern portion. The stripped gravity of the pre-evaporite strata is distinguished by two local lows in the southern part that could be interpreted in terms of gravity as two local troughs on the basement surface. The density models exhibit the presence of an anticlinal structure correlated with Ras Budran oil field, which is surrounded by two fill-sediment grabens from south direction. This confirm that the near-surface bodies are the most affective to obtain a good fit between the observed and calculated profiles.

Keywords

• Gravity stripping
• Well logging
• Gulf of Suez
• Ras Budran
• Bouguer map