Variation in Texture and Strength of Nigerian Tar Sand: Implication for E&P of the Niger Delta Deep Water

D. A. Alao and J. T. Kazeem
Univeristy of Ilorin, Ilorin, Nigeria

Tarsand occurrences around Okitipupa lie within the north-western flank of the Niger Delta. The Nigerian tarsand derives from heavy crude which migrated up dip and impregnated very fine sand in the 120 km by 8 km belt of varying thickness Samples of tarsand were subjected to geotechnical investigation. First, to examine the textural variation in the three varieties (crusty, flexible and friable tarsand) obtained in the field (Loda village, Ode Aye and Ayietoro II in Ondo State).

The second geotechnical investigation carried out was geared toward an understanding of the performance of the tarsand as a binder when mixed with laterite gravel, a sub-base course used in road pavement construction.

The three varieties of tarsand were subjected to chemical treatment to determine the bitumen/ sand ratio of each specimen. Each sand fraction was then subjected to mechanical sieve analysis. The crusty and flexible tarsand specimens were subsequently tested for their bearing strength. Cylindrical Specimens of 100% tarsand were compacted to 10 Kbar pressure and later stressed to failure. Laterite gravel combined with 5%, 10% 15% and 20% by weight of tarsand and compacted at OMC (10% moisture content) were also stressed to failure.

A statistical model which combined the grain size, and strength data was employed to test variation in texture and strength. A pc-compatible software package was adopted for this analysis.

Strength parameters were obtained from the computer print out of the Universal Testing Machine (UTM). These include: Stress peak and strain peak; stress yield and strain yield; stress break and strain break, Young's modulus, load peak, load yield and load break.