A fluid mixing device for mixing a first injection fluid and a second injection fluid includes a first fluid inlet, a second fluid inlet, a mixing chamber in fluid communication with the first and second fluid inlets, and an outlet port in fluid communication with the mixing chamber. The first fluid inlet is configured to conduct the first injection fluid in a first direction and has a first redirecting surface. The second fluid inlet is configured to conduct the second injection fluid in a second direction along a different axis from the first direction and has a second redirecting surface. The mixing chamber is configured to mix the first injection fluid and the second fluid together. The mixture of the first injection fluid and the second injection fluid exits the fluid mixing device via the outlet port.