The significance of fracturing parameters which are aquifer integrity, rock properties, thermal stress, fracturing pressure and produced water quality to alter permeability damage, cake formation and injectivity performance was highlighted in a robust improved internal filtrationhydraulic model and permeability reduction model incorporating a R AT ðcÞ function. The studied system is an injection well multi-reservoir formations. Field data obtained from the log and field reports and improved model were used to simulate injector, fracturing and permeability damage performance. Thus, data requirements in the R AT ðcÞ function which are rock properties, water quality, aquifer integrity, fractures rates and pressures parameters were assessed for its impact on injector performance and permeability damage simulated in MATHLAB and COMSOL multi physics environment. The profile of injector performance and damage reservoir permeability to changes in rock properties and aquifer integrity were demonstrated to have a profound influence on both fracturing phenomena. Thus, sustainable re-injection scheme was shown as a direct consequence of rock mechanics parameters, well hydraulics aquifer integrity that largely depends on the initial concentration of active constituents of the produced water as well as physic-chemical properties of the host aquifer.

An improved produced water reinjection (PWRI) model that incorporates filtration, geochemical reaction, molecular transport, and mass adsorption kinetics was developed to predict cake deposition and injectivity performance in hydrocarbon aquifers in Nigeria oil fields. Thus, the improved PWRI model considered contributions of geochemical reaction, adsorption kinetics, and hydrodynamic molecular dispersion mechanism to alter the injectivity and deposition of suspended solids on aquifer wall resulting in cake formation in pores during PWRI and transport of active constituents in hydrocarbon reservoirs. The injectivity decline and cake deposition for specific case studies of hydrocarbon aquifers in Nigeria oil fields were characterized with respect to its well geometry, lithology, and calibrations data and simulated in COMSOL multiphysics software environment. The PWRI model was validated by comparisons to assessments of previous field studies based on data and results supplied by operator and regulator. The results of simulation showed that PWRI performance was altered because of temporal variations and declinations of permeability, injectivity, and cake precipitation, which were observed to be dependent on active adsorption and geochemical reaction kinetics coupled with filtration scheme and molecular dispersion. From the observed results and findings, transition time t r to cake nucleation and growth were dependent on aquifer constituents, well capacity, filtration coefficients, particle-to-grain size ratio, water quality, and more importantly, particle-to-grain adsorption kinetics. Thus, the results showed that injectivity decline and permeability damage were direct contributions of geochemical reaction, hydrodynamic molecular diffusion, and adsorption kinetics to the internal filtration mechanism, which are largely dependent on the initial conditions of concentration of active constituents of produced water and aquifer capacity.

In mid 2002, the Federal Government of Nigeria through the Special Adviser on Petroleum Matters gave a directive that all Oil and Gas Operators should embark on abandonment and remediation/restoration programs to address all abandoned drill locations cutting across land, swamp and offshore environments. Before this directive, our company operations had commenced a comprehensive effort in 1999 to address these sites. Across the Nigerian Niger Delta, abandoned drill locations (including well stubs) number well over several tens of thousands. The Niger Delta area of the country lies in the southern part of Nigeria and oil and gas operations have been carried out in this region over the past four decades. Community unrests have arisen from lack of commensurate development in this region. In addition, new environmental regulations with very restrictive requirements have been enacted. This case study consists of two phases. The first phase is to address the land sites which involve demolition of existing camp/concrete structures, removal of existing well heads, backfilling of existing pits (including large borrow pits), leveling of entire drill site to match natural contour level, spreading of native humus soil and revegetation with native plant species. The second phase will address the abandoned swamp and offshore wells by ensuring that they are completely plugged and abandoned using a more cost-effective approach such as the use of highly compressed sodium bentonite. Thereafter, the wells will be cut below mudline and removed. This paper discusses the issues involved in abandoning and restoring the land sites and the well stubs in swamp and offshore environments. Experience obtained in carrying along all stakeholders particularly the host communities in the Niger Delta and the regulatory agencies is presented. Other alternatives to pit closure will be mentioned and the environmental and economic benefits of using highly compressed sodium bentonite (Zonite) for plugging well stubs will be discussed. Introduction The Niger Delta is situated on the Gulf of Guinea on the west coast of central Africa (Figure 1). During the Tertiary it was built out into the Atlantic Ocean at the mouth of the Niger-Benue river system, an area of catchment that encompasses more than a million square kilometers of predominantly savannah-covered lowlands. The delta is one of the world's largest, with the subaerial portion covering about 75,000 km2 and extending more than 300 km from apex to mouth (see Figure 1 also). The regressive wedge of clastic sediments which it comprises is thought to reach a maximum thickness of about 12 km. The Niger Delta forms one of the world's major hydrocarbon provinces, with proven ultimate recoverable reserves of approximately 35 billion barrels of oil and an underevaluated, but vast gas resource base. The oil and gas resources are closely associated and are present throughout the delta (see Figure 2). The oils are of the light waxy type, typical of deltas (see Figure 3). Geochemically, they appear to belong to one family, although heavier bacterially degraded oils are found at shallow depths, where the formation temperature is below 80° C. The Need for Closure Before the regulatory directive, the company, based on their ‘Operational Excellence’ philosophy, had pro-actively commenced remediation and restoration of some of these abandoned land sites. By doing so, the company developed improved relationship with major stakeholders. In addition, this effort has gone a long way to solidify their leadership role in the industry from a safety and environmental performance standpoint. History A large number of exploratory wells were drilled on land, swamp and offshore locations. The practice then was the use of Water Based Mud (WBM) and bigger holes. At the land sites, earth materials were borrowed from offsite locations to the drill sites for civil work construction. Large borrow pits were created as a result.

Computational models are developed to predict scale formations, compatibility and injection performance of produced water re-injection in mature hydrocarbon aquifer fields. The models are based on a robust numerical strategy that considered representative K-factors to predict correction for injectivity decline profiles. Simulations in COMSOL Multi-physics environment evaluate scaling effect to determine multi-reservoir commingling phenomenon in matured fields. Results demonstrated that geochemical scaling limit feasible and sustainable water injection performance that could impact petroleum recovery. Fracturing out of water zone was also significant near top and bottom interval cross flow of injection well requiring additional pressure of 100 to 200 psi to initiate fracturing. This requirement excluded fracturing in produce water most re-injection fields with attendant scaling effect.