Method and apparatus for in-situ fluid injector unit

A fluid testing apparatus, comprising:

• a first chamber comprising a testing device that tests a first fluid in the first chamber;
• a second chamber comprising an injection mechanism that injects a second fluid in the second chamber into the first chamber;
• a third chamber;
• a pressure control system that brings the first fluid in the first chamber to a test pressure;
• a first portion separating the first chamber and the second chamber, forming a first high pressure line connecting the first chamber and the second chamber, and enabling a fluid interface between the first fluid and the second fluid located in the first portion;
• a control system to calculate a volume of the second fluid to inject into the first chamber from the second chamber;
• a second portion separating the first chamber and the third chamber, and forming a second high pressure line connecting the first chamber and the third chamber in fluid communication with each other, wherein injecting the volume of the second fluid into the first chamber at a higher pressure than the test pressure displaces an equivalent volume of fluid into the third chamber via the second portion, wherein the equivalent volume of fluid was present in the first chamber prior to injecting the volume of the second fluid;
• and
• a mixing device to mix the volume of the second fluid in the first chamber and a remaining volume of the first fluid in the first chamber to create a combination fluid in the first chamber, the combination fluid having a volume equal to a total volume of the first fluid that was present in the first chamber prior to injecting the volume of the second fluid;
• wherein the testing device tests the combination fluid.