Horseradish peroxidase was injected into the superior colliculus of normal pigmented and albino rats and rats which had been unilaterally enucleated at birth, in order to identify the retinal ganglion cells which contribute normal and abnormal uncrossed retinotectal axons. The results show that while in pigmented rats, the normal uncrossed pathway derives solely from the lower temporal retina and distributes to the anterior and medial parts of the colliculus, occasional cells throughout the retina of albino rats contribute to the uncrossed pathway and the terminal distribution is broader in the tectum. These findings are confirmed with orthograde pathway tracing methods. After neonatal unilateral eye enucleation, many more ganglion cells in the remaining eye of both pigmented and albino rats project ipsilaterally. It is notable from both HRP studies and from further degeneration experiments that cells in part of the lower temporal retina do not restrict their distribution to a mirror togographic position in the ipsilateral tectum but send axons across all but the posterolateral part of the colliculus. No single class of ganglion cell (defined by soma diameter) appears responsible for the expanded ipsilateral projection, although more large cells from the lower temporal retina are involved. These may be the result of enlargement of cells with expanded terminal fields rather than necessarily indicating a preferential contribution from one retinal ganglion cell class.
Most oil and gas producing formations contain clay minerals that were deposited during the sedimentation process, formed during the interaction of heat, pressure, and time on the naturally present minerals in the formation, or precipitated from fluids flowing from one area of the formation to others. The oil and gas industry has extensively investigated the role of these clay minerals during production and the potential permeability damage that can occur with swelling and migration of these clays. For many years, the effective use of salts such as KCl and NaCl in workover fluids for temporary clay stabilization has been well established. However, due to the potential environmental issues and the logistics of using large quantities of salts for this application, many operators have begun to search for alternative clay stabilizer products. This project details the investigation and evaluation of ionic liquids as a clay stabilizer and shale inhibitor additive to prevent clay swelling and migration in comparison to the industry-standard clay stabilizers. Ionic liquids are compounds that are liquids at ambient temperatures and consist entirely of cations and anions, usually a organic cation and a inorganic anion. Screening studies to determine the state of flocculation of clay-bearing fluids and to screen for shale inhibition were conducted with Capillary Suction Time tests (CST), Clay Pack Flow tests and core flow studies. This paper summarizes the results of the clay stabilizer screening studies conducted with ionic liquids and details the effectiveness of the ionic liquids as KCl substitutes, clay stabilizer additives, and shale inhibitors. Introduction It has been reported that approximately 97% of all petroleum reservoirs contain clay minerals. An important consideration with these minerals in the production of oil and gas is to protect the water-sensitive clays and reduce their potential to damage permeability. The two major mechanisms by which clays can cause permeability damage are swelling and migration. When a clay-containing formation comes into contact with a treatment fluid or water that is not in ionic balance with the formation, the clays absorb water into the crystalline structure. This water absorption causes the clays to swell and the particles to increase in volume, plugging the pores in which they reside. In clay migration, the clays can be dispersed by contact with a foreign fluid, or can be dislodged by produced fluids, causing migration thru the formation until a pore throat restriction is encountered. This restriction will cause bridging of the clay particles across the pore throat and result in plugging of the capillary. Clay stabilizing additives can be classified into two categories: temporary and permanent. Temporary clay stabilizing additives are materials that will prevent swelling and migration of clays during drilling, completion, and fracturing operations but will be easily removed by the formation's produced fluids following the treatment. The most common temporary clay stabilizers are simple inorganic cations such as NaCl, KCl, ammonium chloride and calcium chloride. Solutions of 2% to 7% by weight KCl are frequently recommended in treating fluids to minimize the swelling of clays and the migration of nonexpanding type clays. The most recent advances in clay stabilization have been realized in the area of permanent clay stabilizing additives. The most common permanent clay stabilizers are quaternary amine polymers. A monomolecular film of these polymers tightly binds with the clay surface by cation exchange; this film is not removed by the formation's produced fluids following the treatment. The more permanent stabilization is claimed due to the bridging of multiple cationic sites along the polymer chain. These additives leave the formation water-wet, and due to their cationic nature they may be utilized in acidic, neutral, and basic conditions.
Summary Deposition of mineral scales is the root cause of many production problems in oil and gas operations. These scale deposits have resulted in formation damage, production losses, significant rate and pressure reductions, and equipment failure because of corrosion issues. The most commonly encountered mineral scales in the oil field are carbonates and sulfate-based calcium sulfate, barium sulfate, and strontium sulfate scales. However, a more unusual form of these mineral scales, zinc sulfide, has recently been reported. This paper focuses on the systematic study of a zinc sulfide scale and the operation that removed it from a well in the Gulf of Mexico. Identifying the scale form and composition and the factors affecting its dissolution resulted in a treatment that successfully removed the scale, thereby enhancing gas production from the well. This scale was identified as wurtzite, a form of zinc sulfide scale. Extensive laboratory testing considered acid solubility and other scale-removal issues at downhole temperature and pressure conditions, as compared with the theoretical solubility of zinc sulfide in hydrochloric acid (HCl). The study also determined that other factors may affect the real-world dissolution efficiency of the acid: pressure changes, hydrogen sulfide scavenger concentration and type, the ratio of acid volume to scale weight, pre-treatment oxidizer use, and pH values that prevent reprecipitation of dissolved scale. This paper will describe the prejob testing process and a field case history of a coiled-tubing acid scale treatment that effectively removed the zinc sulfide scale from tubulars and the formation. Data will be presented showing the composition of the acid-flow-back samples as well as the treatment and production charts.
This paper was prepared for presentation at the 1999 SPE Mid-Continent Operations Symposium held in Oklahoma City, Oklahoma, 28-31 March 1999.
An aberrant crossed corticotectal pathway can be generated by removal of one visual cortex and the contralateral superior colliculus from newborn rats. This aberrant crossed corticotectal projection arises from the pyramidal neurons located in layer V of the visual cortex and terminates in a spatially orderly manner in the appropriate laminae of the cortically deafferented contralateral colliculus. Comparable results cannot be reproduced by unilateral collicular lesions alone. The significance of these findings and the possible mechanisms involved in the formation of the aberrant pathway are discussed and compared with the retinotectal system.
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