In general, irregular periods are very common during the perimenopause. The most common early menstrual irregularity noticed in the perimenopause is a shortening of cycle length.
Abiogenic petroleum origin. Abiogenic petroleum origin is a term used to describe a number of different hypotheses which propose that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms.
Oil and gas fields are geological features. that result from the coincident occurrence of four types of geologic features (Figure 1): (1) oil and gas source rocks, (2) reservoir rocks, (3) seals, and (4) traps. Each of these. features is discussed and illustrated below and the role of each type of feature in our. natural oil and gas system is emphasized.